glusterd/uss: Create rebalance volfile.

Create a new rebalance volfile, which will not contain
snap-view client translators, irrespective of the status
of USS.

This volfile, will be created and regenerated everytime
the fuse-volfile is generated, and will be consumed
by the rebalance process.

Change-Id: I514a8e88d06c0b8fb6949c3a3e6dc4dbe55e38af
BUG: 1164711
Signed-off-by: Avra Sengupta <asengupt@redhat.com>
Reviewed-on: http://review.gluster.org/9190
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Rajesh Joseph <rjoseph@redhat.com>
Reviewed-by: Atin Mukherjee <amukherj@redhat.com>
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Tested-by: Krishnan Parthasarathi <kparthas@redhat.com>