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/process.go

@@ -0,0 +1,29 @@
+// Copyright (c) 2018 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.
+
+package jaeger
+
+// Process holds process specific metadata that's relevant to this client.
+type Process struct {
+	Service string
+	UUID    string
+	Tags    []Tag
+}
+
+// ProcessSetter sets a process. This can be used by any class that requires
+// the process to be set as part of initialization.
+// See internal/throttler/remote/throttler.go for an example.
+type ProcessSetter interface {
+	SetProcess(process Process)
+}