storage/posix: introduce node-uuid-pathinfo

enabling this option has an effect on pathinfo xattr
request returning <node-uuid>:<path> instead of the
default - which is <hostname>:<path>.

Change-Id: Ice1b38abf8e5df1568bab6d79ec0d53dfa520332
BUG: 765380
Signed-off-by: Venky Shankar <vshankar@redhat.com>
Reviewed-on: http://review.gluster.org/4567
Reviewed-by: Amar Tumballi <amarts@redhat.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>