pathinfo: Provide user namespace access.

Locality can be now queried by unprivileged users with
key "glusterfs.pathinfo".

Setting both "glusterfs.pathinfo" and "trusted.glusterfs.pathinfo"
on disk is prevented with this patch.

Original Author: Vijay Bellur <vbellur@redhat.com>

Change-Id: I4f7a0db8ad59165c4aeda04b23173255157a8b79
Signed-off-by: Vijaykumar M <vmallika@redhat.com>
Reviewed-on: http://review.gluster.org/5101
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>