tests: support regex in EXPECT constructs

            Backport of http://review.gluster.org/6788

Instead of just strings, provide the ability to specify a regex
of the pattern to expect

Change-Id: I288db2290612accd795c3498f74e8b70bab21f2c
BUG: 1115369
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/8235
Reviewed-by: Ravishankar N <ravishankar@redhat.com>
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>