cluster/stripe: don't treat ESTALE as failure in lookup

Problem:
In a stripe volume, symlinks are created only on the first brick via the
default_symlink() call. During gfid lookup, server sends ESTALE from the other
bricks, which is treated as error in stripe_lookup_cbk()

Fix:
Don't treat ESTALE as error in stripe_lookup_cbk()

Change-Id: Ie4ac8f0dfd3e61260161620bdc53665882e7adbd
BUG: 1111454
Signed-off-by: Ravishankar N <root@ravi3.(none)>
Reviewed-on: http://review.gluster.org/8135
Reviewed-by: Raghavendra Bhat <raghavendra@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>