conf: Rework/rename virDomainObjListFindByIDRef

Rework the code such that virDomainObjListFindByID will always
return a locked/ref counted object so that the callers can
always do the same cleanup logic to call virDomainObjEndAPI.
Makes accessing the objects much more consistent.

NB:
There were 2 callers (lxcDomainLookupByID and qemuDomainLookupByID)
that were already using the ByID name, but not virDomainObjEndAPI -
these were changed as well in this update/patch.

Signed-off-by: John Ferlan <jferlan@redhat.com>
Reviewed-by: Jim Fehlig <jfehlig@suse.com>