tests/functional: Add GlusterSD functional test

Add functional testcase for glusterSD. This requires a gluster
volume named 'testvol' running on the same system as this test
runs as a pre-req.

Change-Id: Ibe27b138d78e0922a6455e0984813823a98aeb53
Signed-off-by: Deepak C Shetty <deepakcs@linux.vnet.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/10196
Reviewed-by: Dan Kenigsberg <danken@redhat.com>