seed and lxc seeding & cloning improvements

salt.modules.lxc:
* Add cloning support to lxc.init
* In lxc.bootstrap, start the container before seeding the keys/config to /tmp (failure to do so results in /tmp being wiped out on boot).

salt.runners.lxc:
* More uniform progress reporting and more meaningful return values.

salt.modules.seed:
* in _check_install, use bash if available