Spans don't use parent span's sampled flag when calculating their own sampled value.

[wburningham]

Scenario:

• I have service A that sends a request to service B
• The baggage/tracing information is propagated by service A setting the correct headers
• The "sampled" value from service A is true
• Service B should "honor/use" use the parent span's sampled value (the value from service A) when determining if the span should be sampled.