Fix deadlock in XendDomainInfo when a domain is cleaned up. We are renaming

Fix deadlock in XendDomainInfo when a domain is cleaned up.  We are renaming
the domain, to make it clear that it is a zombie, but this renaming cannot
check the uniqueness of the new name, because this causes a deadlock with
XendDomain.  Instead, we allow the name to be non-unique for the case of
zombie domains.

Change the locking in waitForShutdown and state_set to be robust in the face of
exceptions.

Rename the STATE_VM_ constants to STATE_DOM_.

Signed-off-by: Ewan Mellor <ewan@xensource.com>