xmlrpcTests: refactoring

- split xmlrpcTests into storageTests and virtTests to reduce complexity
- use vdsProxy approach for virtTests part

Change-Id: I683c9e056137e7a189815bf6be2eb79ee80994cf
Signed-off-by: Martin Polednik <mpoledni@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/17893
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Vinzenz Feenstra <vfeenstr@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>