parallels: fix virDomainDefineXML for domain in saved state

parallels: fix virDomainDefineXML for domain in saved state

PCS doesn't store domain config in managed save state file.
It's forbidden to change config for VMs in this state.
It's possible to change config for containers, but after
restoring domain will have that new config, not a config,
which domain had at the moment of virDomainManagedSave.

So we need to handle this case differently from other states.
Let's forbid this operation, if config is changed and if it's
not changed - just do nothing.

Openstack/nova calls virDomainDefineXML on resume with
current domain config, so we can't forbid this operation
in managed save state.

Signed-off-by: Dmitry Guryanov <dguryanov@parallels.com>