glusterd: Improve error logging when a brick from an old volume gets re-used

The error message when creating a volume that contains a brick with
certain xatts set on a parent directory is unclear.

Users do not understand '... or a prefix of it is already part of
a volume'. Most users check the final directory that is used for
a brick, but not its parents.

It would be helpful to present the user with the actual directory that
is preventing the volume to use the brick.

BUG: 923917
Change-Id: I815ad32a992eb0e41ee8fca6ee9327400d042c45
Signed-off-by: Niels de Vos <ndevos@redhat.com>
Reviewed-on: http://review.gluster.org/4701
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>