Posix: Brick failure detection fix for ext4 filesystem

Issue: stat() on XFS has a check for the filesystem status but
ext4 does not.

Fix: Replacing stat() call with open, write and read  to a new file under the
"brick/.glusterfs" directory. This change will work for xfs, ext4 and other
fileystems.

Change-Id: Id03c4bc07df4ee22916a293442bd74819b051839
BUG: 1130242
Signed-off-by: Lalatendu Mohanty <lmohanty@redhat.com>
Reviewed-on: http://review.gluster.org/8213
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>