conf: Use virDomainObjListFindBy*Locked for virDomainObjListAdd

conf: Use virDomainObjListFindBy*Locked for virDomainObjListAdd

Use the FindBy{UUID|Name}Locked helpers which will return a locked
and ref counted object rather than the direct virHashLookup and
virObjectLock of the returned object. We'll need to temporarily
virObjectUnref when we assign a new domain @def, but that will
change shortly when virDomainObjListAddObjLocked returns the
correct reference counted object.

Use the virDomainObjEndAPI in the error path to Unref/Unlock for
the corresponding Unref/Unlock of either the FindBy* return or
the virDomainObjNew since both return a reffed/locked object.

Signed-off-by: John Ferlan <jferlan@redhat.com>
Reviewed-by: Erik Skultety <eskultet@redhat.com>