engine:VDS command to update hook content

VDS command to update content of gluster hook
on a server from the engine.
Gluster hook is identified by gluster command,
stage and name.

Change-Id: I4dc8e12c7d7760114c392db19a56c9cefd4b5763
Signed-off-by: Sahina Bose <sabose@redhat.com>