Fix the side channel attack by using aysnc DnsResolver API with FLAG_NO_CACHE_STORE

Before this CL, FLAG_NO_CACHE_STORE could be used to perform side
channel attack. Because this flag ensures the result is never
added to the cache, but will return a cached response if one exists.
So make FLAG_NO_CACHE_STORE imply FLAG_NO_CACHE_LOOKUP to block the
possibility of side channel attacking.

Bug: 150371903
Test: atest
Change-Id: I37391ffe315b90c0cdfd86888c6bf68b2b89f601