Fix async DNS flag NO_CACHE_STORE doesn't work as expected

The stale cache case isn't handled correctly while performing
cahce_lookup with flag NO_CACHE_STORE, which caused this problem.

Fix it and add a test to ensure it won't happen again.

Test: atest
Bug: 148842821
Change-Id: I72a2211a636cadc72009a5542f7c755c30329c43