Extract the DOM to Drive name, alias and path logic to reusable method

Change-Id: I7389dd8960c9c6245148d9191b2bea5a7e9e4a46
Signed-off-by: Martin Sivak <msivak@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/29059
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-by: Francesco Romani <fromani@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>