Moves this out of ConnectivityService and into each NetworkMonitor
(where it's more self-contained).
Test: as follows
- builds, flashes, boots
- runtest frameworks-net passes
- manual testing with working and non-working hostnames behaves
somewhat (but not entirely) as expected, and not always quickly
Bug: 64133961
Bug: 72345192
Bug: 73872000
Bug: 77140445
Change-Id: Ic4322af3cb49149f2d975cb31f54b2ac7927f907
736353a584