object-storage: Restoring multi volume support in UFO.

* Currently, the users of UFO are restricted to use just one volume
  at any given point of time. This patch removes this limitation.

* The usage of gluster-swift-gen-builders has also changed. With this
  commit the users should mention the list of volumes that they want
  to expose through UFO. So, only the volumes mentioned during the
  ring file generation can be accessed.

  Usage: gluster-swift-gen-builders <vol-name1> [<vol-name2>]...

This is an intermediate fix until we remove the account, container and
object server processes. Once we have this frame work running, it will
completely eliminate the ring files.

Change-Id: I9ad3808519fec9c7c60ad846c4f8b653117a8337
BUG: 909053
Signed-off-by: Mohammed Junaid <junaid@redhat.com>
Reviewed-on: http://review.gluster.org/4485
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Kaleb KEITHLEY <kkeithle@redhat.com>
Reviewed-by: Peter Portante <pportant@redhat.com>