Support faking out the DNS lookups used by NetworkMonitor to
resolve strict mode DNS, and add more test coverage.
These tests were partly adapted from tests we have in Q but
also contain new coverage. This is because in Q the interface
between ConnectivityService and NetworkMonitor changed
substantially, and it is impractical to backport
NetworkMonitorTest.
Bug: 122652057
Test: atest FrameworksNetTests
Change-Id: I6497b7efa539267576d38d3036eef0af0df4e9cb
Merged-In: Iaa78a7edcf23755c89d7b354edbc28d37d74d891
7c9b1c757a