Reworked tests tree.

* The conftest file is now in the galah.tests package which is one
  of the recommended locations per the py.test docs.
* The pyredis plugin is now in a more general location and should be
  usable throughout the testing tree now.
* OpenVZ no longer requires a command line option to enable and instead
  figures out whether it should run by loading the config and checking
  to see if vzctl is installed. I may do a similar thing to the redis
  plugin in the future.
Moved the bootstrapper plugin.

* This wasn't necessary, but the inconsistency of having the
  bootstrapper pluging apart from the other plugin was bothering me.