initial ovirt support

This patch provides initial ovirt support.  Some changes and issues include:

* I added `domain` as an attribute to the oVirt provider; so instead of logging in with a username of `admin@internal`, you would specify the `domain` as `internal` and have the user login as `admin`.  This seems to match the web UI.

* The workflow seems to be slightly different; it's:
   * create VM
   * start VM
   * stop VM
   * delete VM

The first two steps can be combined into the `launch` method; however, stopping a VM takes some time, so the last two steps cannot be combined into `destroy`.  As a result, the `destroy` method currently only tries to delete the VM, and will fail because the VM is not yet stopped.

I tihnk the solution is to consider the *stop VM* step to be equivalent to `pause`; and have the oVirt workflow be `start` > `pause` > `destroy`.  What do others think?