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/doc.go

@@ -0,0 +1,24 @@
+// Copyright (c) 2017 Uber Technologies, Inc.
+//
+// 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.
+
+/*
+Package jaeger implements an OpenTracing (http://opentracing.io) Tracer.
+It is currently using Zipkin-compatible data model and can be directly
+itegrated with Zipkin backend (http://zipkin.io).
+
+For integration instructions please refer to the README:
+
+https://github.com/uber/jaeger-client-go/blob/master/README.md
+*/
+package jaeger