Tracing through the Broker - incoming request has a Trace ID

[Harwayne]

Problem
A request made to the Broker, with a Trace ID present, should continue that trace through the Broker and via any replies.

Persona:
Event Producer

Exit Criteria
The following curl sent from inside the cluster results in a single trace that shows the Broker ingress, the underlying Channel, all the Triggers, and replies back through the Broker. It should have at least one level of replies. The trace must be viewable via Zipkin, Jaeger, or Stackdriver.

traceId=$(cat /proc/sys/kernel/random/uuid)
traceId="${traceId//-/}"

eventId=$(cat /proc/sys/kernel/random/uuid)

curl -v "http://default-broker.default.svc.cluster.local" \
  -X POST \
  -H "X-B3-Traceid: ${traceId}" \
  -H "X-B3-Spanid: ${traceId:16}" \
  -H "X-B3-Flags: 1" \
  -H "ce-specversion: 0.2" \
  -H "ce-type: ${eventType}" \
  -H "ce-time: 2018-04-05T03:56:24Z" \
  -H "ce-id: ${eventId}" \
  -H "ce-source: ${eventSource}" \
  -H 'Content-Type: application/json' \
  -d '{ "much": "wow" }'

[Harwayne]

/project Observability To do

[Harwayne]

/milestone v0.10.0

[ian-mi]

/close tracing conformance tests are passing for both ChannelBasedBroker and MTChannelBasedBroker