uml: s/virDomainObjListFindByID/virDomainObjListFindByUUID/
    
    ListFindByID() still requires to step through items in the hash table
    (in the worst case scenario through all of them), lock each one and
    compare whether we've found what we're looking for. This is suboptimal
    as locking a domain object means we need to wait for the current API
    running over the object to finish.
    
    Unfortunately, we can't drop the function completely because we have
    this public API virDomainLookupByID which we can't drop.
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>