tests: Add blockSD tests

Add test for the metadataValidity before modiying its confusing
implementation.

Change-Id: I31838ac5847e464ee6ba3e1b3bd85312b4f9cee7
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/25207
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>