Fix for test usst.t and bug-1167580-set-proper-uid-and-gid-during-nfs-access.t

Fix for test usst.t and bug-1167580-set-proper-uid-and-gid-during-nfs-access.t

testcase usst.t and
bug-1167580-set-proper-uid-and-gid-during-nfs-access.t
uses below method to generate random string
cat /dev/urandom | tr -dc 'a-zA-Z' | fold -w 8 | head -n 1

Doing a cat on /dev/urandom can consume more CPU usage.

Change to:
uuidgen | tr -dc 'a-zA-Z' | head -c 8

Change-Id: I9cb562557ae860026fb5e140ed9b5e297b4428d9
BUG: 1163543
Signed-off-by: vmallika <vmallika@redhat.com>
Reviewed-on: http://review.gluster.org/9703
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Tested-by: Krishnan Parthasarathi <kparthas@redhat.com>