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/Gopkg.toml

@@ -0,0 +1,27 @@
+[[constraint]]
+  name = "github.com/crossdock/crossdock-go"
+  branch = "master"
+
+[[constraint]]
+  name = "github.com/opentracing/opentracing-go"
+  version = "^1"
+
+[[constraint]]
+  name = "github.com/prometheus/client_golang"
+  version = "0.8.0"
+
+[[constraint]]
+  name = "github.com/stretchr/testify"
+  version = "^1.1.3"
+
+[[constraint]]
+  name = "github.com/uber-go/atomic"
+  version = "^1"
+
+[[constraint]]
+  name = "github.com/uber/jaeger-lib"
+  version = "^1.3"
+
+[[constraint]]
+  name = "go.uber.org/zap"
+  version = "^1"