Migrate DnsUtilsTest to the NetworkMonitor version of FakeDns.

There are two versions of FakeDns in the tree. This test uses the
less capable one. Migrate it to the more capable one that is also
used by NetworkMonitorTest.

This is in preparation for unifying the two versions of FakeDns
into one.

Bug: 240259333
Test: test-only change
Change-Id: I6f4652937c6107983605487d1ca9bf393f78dc66
2 files changed