Raspberry Pi kernel finally supports all the bits required by LXC [1]

This patch makes "./configure --with-distro=raspbian" to install lxcbr0
based config file and upstart jobs.
Also src/lxc/lxc.net now checks the existence of the lxc-dnsmasq user
(and fallbacks to dnsmasq)

RPI users still need to pass
"MIRROR=http://archive.raspbian.org/raspbian/" parameter to lxc-create
to pick the correct packages

MIRROR=http://archive.raspbian.org/raspbian/ lxc-create -t debian -n rpi

[1] https://github.com/raspberrypi/linux/issues/176

stable-1.0: Cherry-picked from master minus the lxc-net change as
lxc-net isn't available in LXC 1.0.x. Instead it is assumed that the
distribution will take care of setting up the network (lxcbr0 in this
case).
Signed-off-by: S.Çağlar Onur <caglar@10ur.org>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>