test/uss : activate the snapshot after creating.

Till now we were activating the snapshot along with the snapshot create.
But one of the recent patches has changed that behavior. Now we have
to explicitly issue activate-on-create using snapshot config if we
want snapshot to be activated during snapshot create.

Till patch fixes the regression failure which is seen lately.

Change-Id: Ic53b16e22569e521bd70dd3bfa7154a0424151ce
BUG: 1155042
Signed-off-by: Sachin Pandit <spandit@redhat.com>
Reviewed-on: http://review.gluster.org/9113
Reviewed-by: Rajesh Joseph <rjoseph@redhat.com>
Reviewed-by: Meghana M <mmadhusu@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Kaushal M <kaushal@redhat.com>