Adjust VM xml to support iso streaming

The newer libvirt version (1.1.2) has support for iso streaming.
The virtual machine xml must be as following:

    <disk type='network' device='cdrom'>
      <source protocol='{ftp|http}' name='/url/path'>
        <host name='host.name' port='{21|80}'/>
      </source>
    </disk>

Signed-off-by: Aline Manera <alinefm@br.ibm.com>
Create sanity test to verify libvirt supports iso streaming

It is needed to enable/disable the iso streaming feature.
For that, libvirt must support it.
This test should be used while exposing the host capabilities.
It is the same test I created to libvirt community.

Signed-off-by: Aline Manera <alinefm@br.ibm.com>