New local provider changes land in trunk - quantal users beware

[Clint Byrum]

So, after some testing and reviews, an overhaul of the local provider has
landed in trunk! Thanks to Kapil for getting the ball rolling on that,
and for the review of the finished product.

This change switches the local provider to use the Ubuntu Cloud Images
instead of building a minimal chroot with debootstrap. This brings the
local provider closer in line with the other providers. This also means
that you are more likely to have an up to date container on deploy. This
also may end up being a bit of a regression because it is a bit slower
to untar and upgrade the cloud image than it was to just copy and boot
an out of date chroot.

The change also switches to using lxc's built in bridge, rather than
libvirt for networking. This means that libvirt is no longer a dependency
of juju, and it also means juju can play nicely with existing libvirt
setups.

We've also removed all upstart jobs from the local provider, so there
shouldn't be issues with the machine agent spinning out of control on
reboot. It also won't leave anything behind if you reboot other than
stale pid files in the data-dir.

With this change, Ubuntu 11.10 users will need a backported ubuntu-cloud
LXC template to use the local provider. 11.10 users are encouraged to
update to 12.04, but if you are stuck on 11.10 it may be better to use
juju 0.5.2 from the 0.5 PPA.

Unfortunately, while testing this extensively, I ran into this kernel
bug in quantal quite a bit:

https://bugs.launchpad.net/ubuntu/quantal/+source/linux/+bug/1021471

The bug seems to be mostly understood now (its really two bugs) and I
hope that fixes will be released for quantal's kernel ASAP. The workaround
for users with a 'wl' based wireless chipset is to use an older kernel (I
use 3.4.12 from the upstream kernel PPA, but precise's kernels might work
too). For non-wl users a newer kernel should work fine (3.6 for instance).

This should be the final change that lands in "honolulu" (0.6). I will
keep trunk open for bug fixes only until Tuesday (conveniently after
the US holiday Columbus Day). After that, 0.6 will be released. I've
gone ahead and uploaded trunk to the 0.6 PPA now. On release day it will
receive 0.6 and then only be updated for 0.6.x series releases.