tests: add initial tests for clientIF

This patch adds the tests for prepareVolumePath,
and prepares the infrastructure for more clientIF tests.

Relates-To: http://gerrit.ovirt.org/22928/
Change-Id: Iad652aed46b9fe985d7143052bd26320970502b5
Signed-off-by: Francesco Romani <fromani@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/24614
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>