This solves the problem reported in #331 with needing to specify
--provider=lxc to use the LXC provider in an Ubuntu Linux environment;
additionally, it adds the LXC option needed to run LXC on Ubuntu
15.10, but not on 14.04 where that option is unavailable and would
totally break LXC.
By default we are placed inside a virtualenv by the .bash_profile using
/usr/bin/python forces the provisioning script to run outside of this
virtualenv.