OpenTracing trace context should cope with Hystrix using separate thread

When using OpenTracing with Hystrix, the default Hystrix configuration uses a separate thread for the outbound request.

Currently the trace context from the route is not carried across to this new thread, causing the outbound request to be recorded in a separate trace instance.

Need to ensure that the trace context is carried to the new thread/exchange.

As a workaround, the Hystrix configuration property executionIsolationStrategy should be set to "SEMAPHORE".