cluster/afr: Sparse file self-heal canges

- Fix boundary condition for offset
- Honour data-self-heal-algorithm option
- Added tests for sparse file self-healing

Change-Id: I14bb1c9d04118a3df4072f962fc8f2f197391d95
BUG: 1080707
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/7339
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>