tests: metadata self-heal tests

        Backport of http://review.gluster.org/8515

BUG: 1136826
Change-Id: Iebbf5ac58e7bf884221638ad10b19dee60b6ea56
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/8591
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Ravishankar N <ravishankar@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>