cluster/afr: fsync before erase xattrs in data self-heal

Added extra fsync to data self-heal code to make sure the
data reached disk before erasing the changelogs

Change-Id: I9e7e6e55cdc49de2b991705d1638946464a9d4f9
BUG: 927146
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/4744
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>