opentracing -> opencensus (#802)

* update vendor directory, add go.opencensus.io

* update imports

* oops

* s/opentracing/opencensus/ & remove prometheus / zipkin stuff & remove old stats

* the dep train rides again

* fix gin build

* deps from last guy

* start in on the agent metrics

* she builds

* remove tags for now, cardinality error is fussing. subscribe instead of register

* update to patched version of opencensus to proceed for now TODO switch to a release

* meh

fix imports

* println debug the bad boys

* lace it with the tags

* update deps again

* fix all inconsistent cardinality errors

* add our own logger

* fix init

* fix oom measure

* remove bugged removal code

* fix s3 measures

* fix prom handler nil

vendor/github.com/openzipkin/zipkin-go/noop.go

@@ -0,0 +1,25 @@
+package zipkin
+
+import (
+	"time"
+
+	"github.com/openzipkin/zipkin-go/model"
+)
+
+type noopSpan struct {
+	model.SpanContext
+}
+
+func (n *noopSpan) Context() model.SpanContext { return n.SpanContext }
+
+func (n *noopSpan) SetName(string) {}
+
+func (*noopSpan) SetRemoteEndpoint(*model.Endpoint) {}
+
+func (*noopSpan) Annotate(time.Time, string) {}
+
+func (*noopSpan) Tag(string, string) {}
+
+func (*noopSpan) Finish() {}
+
+func (*noopSpan) Flush() {}