swarm: integrate OpenTracing; propagate ctx to internal APIs (#17169)

* swarm: propagate ctx, enable opentracing

* swarm/tracing: log error when tracing is misconfigured

vendor/github.com/uber/jaeger-client-go/CONTRIBUTING.md

@@ -0,0 +1,170 @@
+# How to Contribute to Jaeger
+
+We'd love your help!
+
+Jaeger is [Apache 2.0 licensed](LICENSE) and accepts contributions via GitHub
+pull requests. This document outlines some of the conventions on development
+workflow, commit message formatting, contact points and other resources to make
+it easier to get your contribution accepted.
+
+We gratefully welcome improvements to documentation as well as to code.
+
+# Certificate of Origin
+
+By contributing to this project you agree to the [Developer Certificate of
+Origin](https://developercertificate.org/) (DCO). This document was created
+by the Linux Kernel community and is a simple statement that you, as a
+contributor, have the legal right to make the contribution. See the [DCO](DCO)
+file for details.
+
+## Getting Started
+
+This library uses [glide](https://github.com/Masterminds/glide) to manage dependencies.
+
+To get started, make sure you clone the Git repository into the correct location
+`github.com/uber/jaeger-client-go` relative to `$GOPATH`:
+
+```
+mkdir -p $GOPATH/src/github.com/uber
+cd $GOPATH/src/github.com/uber
+git clone git@github.com:jaegertracing/jaeger-client-go.git jaeger-client-go
+cd jaeger-client-go
+```
+
+Then install dependencies and run the tests:
+
+```
+git submodule update --init --recursive
+glide install
+make test
+```
+
+## Imports grouping
+
+This projects follows the following pattern for grouping imports in Go files:
+  * imports from standard library
+  * imports from other projects
+  * imports from `jaeger-client-go` project
+  
+For example:
+
+```go
+import (
+	"fmt"
+ 
+	"github.com/uber/jaeger-lib/metrics"
+	"go.uber.org/zap"
+
+	"github.com/uber/jaeger-client-go/config"
+)
+```
+
+## Making A Change
+
+*Before making any significant changes, please [open an
+issue](https://github.com/jaegertracing/jaeger-client-go/issues).* Discussing your proposed
+changes ahead of time will make the contribution process smooth for everyone.
+
+Once we've discussed your changes and you've got your code ready, make sure
+that tests are passing (`make test` or `make cover`) and open your PR. Your
+pull request is most likely to be accepted if it:
+
+* Includes tests for new functionality.
+* Follows the guidelines in [Effective
+  Go](https://golang.org/doc/effective_go.html) and the [Go team's common code
+  review comments](https://github.com/golang/go/wiki/CodeReviewComments).
+* Has a [good commit message](https://chris.beams.io/posts/git-commit/):
+   * Separate subject from body with a blank line
+   * Limit the subject line to 50 characters
+   * Capitalize the subject line
+   * Do not end the subject line with a period
+   * Use the imperative mood in the subject line
+   * Wrap the body at 72 characters
+   * Use the body to explain _what_ and _why_ instead of _how_
+* Each commit must be signed by the author ([see below](#sign-your-work)).
+
+## License
+
+By contributing your code, you agree to license your contribution under the terms
+of the [Apache License](LICENSE).
+
+If you are adding a new file it should have a header like below.  The easiest
+way to add such header is to run `make fmt`.
+
+```
+// Copyright (c) 2017 The Jaeger Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+```
+
+## Sign your work
+
+The sign-off is a simple line at the end of the explanation for the
+patch, which certifies that you wrote it or otherwise have the right to
+pass it on as an open-source patch.  The rules are pretty simple: if you
+can certify the below (from
+[developercertificate.org](http://developercertificate.org/)):
+
+```
+Developer Certificate of Origin
+Version 1.1
+
+Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
+660 York Street, Suite 102,
+San Francisco, CA 94110 USA
+
+Everyone is permitted to copy and distribute verbatim copies of this
+license document, but changing it is not allowed.
+
+
+Developer's Certificate of Origin 1.1
+
+By making a contribution to this project, I certify that:
+
+(a) The contribution was created in whole or in part by me and I
+    have the right to submit it under the open source license
+    indicated in the file; or
+
+(b) The contribution is based upon previous work that, to the best
+    of my knowledge, is covered under an appropriate open source
+    license and I have the right under that license to submit that
+    work with modifications, whether created in whole or in part
+    by me, under the same open source license (unless I am
+    permitted to submit under a different license), as indicated
+    in the file; or
+
+(c) The contribution was provided directly to me by some other
+    person who certified (a), (b) or (c) and I have not modified
+    it.
+
+(d) I understand and agree that this project and the contribution
+    are public and that a record of the contribution (including all
+    personal information I submit with it, including my sign-off) is
+    maintained indefinitely and may be redistributed consistent with
+    this project or the open source license(s) involved.
+```
+
+then you just add a line to every git commit message:
+
+    Signed-off-by: Joe Smith <joe@gmail.com>
+
+using your real name (sorry, no pseudonyms or anonymous contributions.)
+
+You can add the sign off when creating the git commit via `git commit -s`.
+
+If you want this to be automatic you can set up some aliases:
+
+```
+git config --add alias.amend "commit -s --amend"
+git config --add alias.c "commit -s"
+```