glusterd: Mark vol as deleted by renaming voldir before cleaning up the store

PROBLEM:

During 'volume delete', when glusterd fails to erase all information
about a volume from the backend store (for instance because rmdir()
failed on non-empty directories), not only does volume delete fail on
that node, but also subsequent attempts to restart glusterd fail
because the volume store is left in an inconsistent state.

FIX:

Rename the volume directory path to a new location
<working-dir>/trash/<volume-id>.deleted, and then go on to clean up its
contents. The volume is considered deleted once rename() succeeds,
irrespective of whether the cleanup succeeds or not.

Change-Id: Iaf18e1684f0b101808bd5e1cd53a5d55790541a8
BUG: 889630
Signed-off-by: Krutika Dhananjay <kdhananj@redhat.com>
Reviewed-on: http://review.gluster.org/4639
Reviewed-by: Amar Tumballi <amarts@redhat.com>
Reviewed-by: Kaushal M <kaushal@redhat.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>