Add tests to cover repeated setResolverConfiguration

Two tests are added to protect the resolver when it continually
receives the same setup requests.

When the resolver receives repeated and same setup:
[1] Do not clear the cache.
[2] Do not clear the stats (the stats for cleartext DNS servers
    got from GetResolverInfo()).
[3] Do not start a new re-evaluation process for the private DNS
    servers if they have been marked as in_progress.
[4] Need not to re-validate the private DNS servers if they have
    been validated.

Another test is added to protect the implementation of aosp/1108695.

Fix: 150678049
Test: resolv_integration_test passed
Change-Id: I7a866e7e305c0fb703ccb9546d1c70ce77e2d3c7