glusterd: Add a cmd for getting uuid of local node

Usage: gluster system:: uuid get

This is needed since we generate uuid of a node in a lazy manner. ie, we
generate a uuid for the node only on the first volume or peer operation,
when the node needs an external identity.  With this command, we can
force[1] the uuid generation, without a volume or peer operation performed.

[1]: Querying for uuid (or uuid get), forces uuid to come into
existence.

Change-Id: I62c8b6754117756aa4d773dd48af4ddeb1a1d878
BUG: 971661
Signed-off-by: Krishnan Parthasarathi <kparthas@redhat.com>
Reviewed-on: http://review.gluster.org/5175
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Kaushal M <kaushal@redhat.com>