vz: Use virDomainObjListFindBy{UUID|ID}Ref

vz: Use virDomainObjListFindBy{UUID|ID}Ref

For vzDomainLookupByID and vzDomainLookupByUUID let's
return a locked and referenced @vm object so that callers
can then use the common and more consistent virDomainObjEndAPI
in order to handle cleanup rather than needing to know that the
returned object is locked and calling virObjectUnlock.

The LookupByName already returns the ref counted and locked object,
so this will make things more consistent.

Also adjust the prlsdkHandle{VmState|VmRemoved|Perf}Event APIs
in the same manner.

Signed-off-by: John Ferlan <jferlan@redhat.com>
Reviewed-by: Nikolay Shirokovskiy <nshirokovskiy@virtuozzo.com>