Code review comment for lp:~javier.collado/utah/provisioned_machine

Max, I've applied the following changes based on your comments:

- ProvisionedMachine class implementation has been moved to ssh module as
  suggested. provisioning.py is already quite large, so I prefer to do that
  rather than moving ssh mixin back.

- self.clean instance attribute has been added to the ProvisionedMachine
  implementation to fix the problem that I had when calling the cleanup
  methods. Indeed, there was no need to overwrite __del__ implementation.

Besides this, I've changed a little bit the timeout behavior of {ping,ssh}check
methods (have a look at rev. 816 commit message or the updated documentation in
the code).