glusterd: Changes to provide interface for USS

The changes which consists of the translators for the USS (User Servicable
Snapshots) is submitted as a separate patch. Current patch provides the
CLI access to the feature.

Change-Id: I6b98a42fcfa82f0870d8048fe0bb53141565e9c6
BUG: 1094815
Signed-off-by: Varun Shastry <vshastry@redhat.com>
Reviewed-on: http://review.gluster.org/7705
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Atin Mukherjee <amukherj@redhat.com>
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Tested-by: Krishnan Parthasarathi <kparthas@redhat.com>