Virt test simple

Simplified version of the work I started, after inspiration (and code) from Stefan and Luiz.

Good news:

* It doesn't use aexpect!
* It does use fabric (wrapped in the remote module)!

A good deal of this should actually live outside avocado, on a virt plugin and virt-tests, but I wanted something that could be convenient to test. You need a little setup:

    mkdir -p ~/avocado/data/images/
    cd ~/avocado/data/images/
    wget https://lmr.fedorapeople.org/jeos/jeos-20-64.qcow2.7z
    7za e jeos-20-64.qcow2.7z

Then you should be good to go.