USS: initialize a list before using it.

backport of the patch http://review.gluster.org/8569 by
Raghavendra G <rgowdapp@redhat.com>

Change-Id: I7b25fdf27c6d7ff66d24925bc73d9c6681259d37
BUG: 1143961
Signed-off-by: Raghavendra Bhat <raghavendra@redhat.com>
Reviewed-on: http://review.gluster.org/8764
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>