[OWL-770] refine func getExistedHosts()
[OWL-770] refine func getExistedHosts()

masato25/open-falcon-backend,masato25/open-falcon-backend,masato25/open-falcon-backend,masato25/open-falcon-backend,masato25/open-falcon-backend,Cepave/open-falcon-backend,Cepave/open-falcon-backend,Cepave/open-falcon-backend,Cepave/open-falcon-backend,masato25/open-falcon-backend,Cepave/open-falcon-backend,Cepave/open-falcon-backend