Disable fallocate for  Gluster volumes

The overridden configuration files of gluster now disable the usage of
fallocate. Also modified the functional test configuration files
accordingly.

BUG: 951661
Change-Id: I3c7d518e0415b7eea5b31c88dd647069f9d730ac
Signed-off-by: Chetan Risbud <crisbud@redhat.com>
Signed-off-by: Luis Pabon <lpabon@redhat.com>
Reviewed-on: http://review.gluster.org/5303