Support jaeger-debug-id header even when there is an established trace context

[yurishkuro]

Some command line tools like yab are capable of starting a trace before sending the request. They also allow setting additional headers like jaeger-debug-id, but the Jaeger client libs ignore (at least Java client does) it since there is already a trace context.

• make sure all clients respect the header regardless of the presence of the trace
• add a test for this behavior to end-to-end test

[vprithvi]

This is true of the node client as well.
Additionally, we should test that the trace id/span id in the trace context isn't mutated by application of jaeger-debug-id

[rbtcollins]

I suspect this is true of the c++ client too since our nginx stack seems to be ignoring the header.

[yurishkuro]

Per #3362, we're sunsetting Jaeger clients.