Add lxc to our cloud-init packages

Add lxc to our cloud-init packages

However don't add lxc if the machine itself is an
lxc container as the install fails on precise causing
the lxc container to fail to start.

https://code.launchpad.net/~thumper/juju-core/lxc-cloud-init/+merge/169328

Requires: https://code.launchpad.net/~thumper/juju-core/machine-id-from-tag/+merge/169327

(do not edit description out of merge proposal)

[thumper, 2013-06-14 02:36:30]

Please take a look.

[fwereade, 2013-06-14 07:55:22]

Needs a CheckPackage in a test somewhere

[jameinel, 2013-06-16 08:38:44]

LGTM caveat William's request.

[thumper, 2013-06-16 23:45:55]

Please take a look.

[dave_cheney.net, 2013-06-16 23:47:51]

LGTM. Thanks for the test.

[serge.hallyn, 2013-06-18 14:32:21]

Hi,

Not installing lxc by default if you're already inside a container is
reasonable, since you may well not have been able to control the environment of
the first container.

However, if you are able to control the creation of the first container (as you
are in juju), then you can make lxc installable inside that container.  It
amounts to:

1. set lxc.aa_profile = lxc-container-default-with-nesting
2. set lxc.mount.hook = /usr/share/lxc/hooks/mountcgroups
3. the lxc package should set up a lxcbr0 which does not conflict with the
parent container's address.  The saucy package does this by default.  If it is
needed, we could try to SRU that change to precise's lxc.  Alternatively, you
could hack the lxc network configuration settings by hand (from cloud-init or
from juju install script) by either modifying /etc/default/lxc after the fact,
or creating a suitable one ahead of time so that lxc does not overwrite it on
install.

cloud-init can detect that 1 and 2 are satisified ( by looking at
/proc/1/attr/current to check the aa profile and by checking whether cgroups are
mounted).