JSCBC-76: Added support for replica-read.

Added getReplica and getReplicaMulti methods to do document
retrieval from replica nodes.

Change-Id: I1414e03ed05047a72ada629ef6558d7742a6b307
Reviewed-on: http://review.couchbase.org/30041
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Brett Lawson <brett19@gmail.com>