Add fabric_dict:is_key/2

BugzId: 21755
Implement fabric_util:stream_start/2

This is a utility function that handles gathering the start of a rexi
stream. It will return a single full hash ring of shards or an error.

BugzId: 21755
Update _all_docs coordinator to use new RPC APIs

BugzId: 21755
Update map view coordinator to use new RPC APIs

BugzId: 21755
Update reduce view coordinator to use new RPC APIs

BugzId: 21755
Remove test for old reduce view behavior

This test is no longer valid because its checking that a complete
message removes other workers from the same range which no longer
happens. This is because fabric_util:stream_start/2 now removes all
workers and returns us a single complete shard ring.

BugzId: 21755
Update _changes coordinator to use new RPC APIs

BugzId: 21755