Strip out the lxd options

[tonyandrewmeyer]

The intention was to isolate my system from the crazy things some of the unit tests do, but it's complicated and slow and the per-charm version in particular is not working correctly.

It would be better to rip this out completely and just run super-tox itself inside of a VM, and assume that they aren't going to cross-contaminate each other.

If it's worth coming back to this, then probably using the spread system would make more sense.