MB-9312: Implement server grouping

Support the following functions:
-create
-delete
-rename
-list
-addServers
-moveServers

Change-Id: I6728f146209a07c104ba69a337cf8dd001a1fe51
Reviewed-on: http://review.couchbase.org/30066
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Bin Cui <bin.cui@gmail.com>
Tested-by: Bin Cui <bin.cui@gmail.com>