The `with sh.sudo` pattern that we were using in python-sh was
deprecated, and emperically hangs on Ubuntu xenial. Since in general
the use of python-sh/python-pbs caused trouble (requiring extra
dependencies, confusing syntax), this just removes it.
We replace it with a new zulip_tools.py library function that echoes
the command line and streams the output.
We do the same to install-phantomjs so we can remove that dependency.
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.
Tim Abbott
Jason Michalski
Luke Faraone