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 (this is necessary since /tmp may be 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