Add Ceilometer docs gate

This fixes bug #1063805

Change-Id: I63b42104d88ed96f5a2bd42b621d5eb7ff483aaa
Signed-off-by: Julien Danjou <julien@danjou.info>
Reviewed-on: https://review.openstack.org/18954
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins