ureadahead should not run in containers

when I type 'poweroff' in a natty container, I sometimes (not always) see:

umount2: Device or resource busy
umount: /var/lib/ureadahead/debugfs busy - remounted read-only
   ...done.
mount: / is busy
 * Will now halt

Don't see this with oneiric or lucid containers.

ureadahead should not run at all in a container.

Disabling it in a container should be done in the same way as will be done for skipping select mounts in mountall. The intent is that it will be done as part of the servercloud-p-lxc blueprint.

Now that upstart will now about containers, ureadahead should not run if in a container.

Fix commited to the packaging branch, however this requires the new upstart which hasn't finished building on armel, armhf and powerpc, so I won't be uploading it just yet.

Actually just reverted as it'd break ureadahead entirely as ureadahead starts so early that it's run before container-detect.

As discussed with Serge on IRC, actually going with won't fix.
As far as I can tell, ureadahead is actually doing what it should and this bug was a problem when lxc was waiting for all processes to go away on shutdown. With the new kernel, this is no longer the case, so this change shouldn't be needed anymore.