Add bypass private DNS test case and null network test for DnsResolver cts

1. add test case for testing bypass Private DNS
2. add null network test
3. minor change for cleanup

Bug: 130594022
Test: atest DnsResolverTest

Merged-In: I8dd48f11baf92d953ded237204a3c2cd3b58581d
(cherry picked from commit da665a0a78a2919c3e2edabafec463de3de9ddb7)

Change-Id: Iabb100c51fd80eca5ab0284bc891f4fb98492e8b
1 file changed
tree: c22619f3b0ffc5bf6d69dc31bf1f59a90d9c8d28
  1. tests/