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.

    $ scripts/avocado run tests/qemu/boot.py
    JOB ID    : cd234702abc8e5b17aa5cd73be0648b12ac62d06
    JOB LOG   : /home/lmr/avocado/job-results/job-2014-08-30T00.20-cd23470/job.log
    TESTS     : 1
    (1/1) tests/qemu/boot.py: PASS (6.74 s)
    PASS      : 1
    ERROR     : 0
    FAIL      : 0
    SKIP      : 0
    WARN      : 0
    NOT FOUND : 0
    TIME      : 6.74 s