conf: Fix error path logic in virDomainObjListAddLocked

conf: Fix error path logic in virDomainObjListAddLocked

If the virHashAddEntry fails, then we need to "careful" about
how we free the @vm. When virDomainObjNew returns there is one
reference and the object is locked, so use virDomainObjEndAPI
when done.

Add a virObjectRef in the error path for the second virHashAddEntry
call since it doesn't call virObjectRef, but virHashRemoveEntry
will call virObjectUnref because virObjectFreeHashData is called
when the element is removed from the hash table as set up in
virDomainObjListNew.

Eventually these paths should goto error and error should be changed
to use EndAPI as well, but that requires more adjustments to other
paths in the code to have a locked and ref counted @vm.

Signed-off-by: John Ferlan <jferlan@redhat.com>