Review GetFromReplica implementation

During team call, the intent and schematics of GetFromReplica was discussed and the .NET implementation needs to be reviewed.

The GetFromReplica schematics should be:

• should attempt to get document from active and all configured replicas
• return the first result
• cancelling / ignore the remainder
• (alternative is to return all results and allow consumer to decide which to use)?

The current implementation seems to schedule the active request first, then synchronously request the replicas in a foreach loop (not using the same mechanism as for active).