Baggage items are not propagated from parent's span context

[rgeorgiev]

According to OpenTracing spec: https://github.com/opentracing/specification/blob/master/specification.md

All baggage items has to be propagated to all child SpanContexts, but looking at
WavefrontSpanBuilder.createSpanContext() they are not propagated.

[vikramraman]

Thanks for raising this issue @rgeorgiev. We will address it for the next release.

[vikramraman]

Done.