Tests: Added function to get pending heal count from heal-info

Change-Id: I0aed0bb79e45326e3872ae187cb9addd06342a56
BUG: 861015
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/4399
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>