Adding new unit tests and removed some unused functions

New unit tests help improve test coverage of common/Glusterfs.py code
Also removed a function that was no longer being used.

Change-Id: Iaa0eed3d2b9ffcc148c1e00b28322ebf93b3f13c
Signed-off-by: Thiago da Silva <thiago@redhat.com>
Reviewed-on: http://review.gluster.org/6053
Reviewed-by: Luis Pabon <lpabon@redhat.com>
Tested-by: Luis Pabon <lpabon@redhat.com>