Pass vdi_ref to fake.create_vbd() not a string
Pass vdi_ref to fake.create_vbd() not a string

This would not cause a problem since vdi_ref wasn't used internally in
the fake xenapi module. At least not yet...

Change-Id: I2fe094b9c3a7d478fe20149a368af132f3258bda

n0ano/ganttclient