In case creating a VM fails before the OP_INSTANCE_CREATE job is
enqueued in Ganeti, the VM and its NICs must be deleted, and the
resources must be released from Quotaholder, which is exactly what is
done when a VM is deleted from Ganeti. Instead of duplicating the code,
this commit uses the same function that is used by snf-dispatcher, by
mocking an successfully OP_INSTANCE_REMOVE.