tests: Small corrections in cases

Changes include:
- disable use of std::cout in DNS test case (use BOOST_TEST_MESSAGE instead)
- renaming test suites for InMemoryStorage cases.  All InMemoryStorage
  cases are grouped under InMemoryStorage super-suite and specific
  implementations are put in Common, Fifo, Lru, Lfu, Persistent suites.

Change-Id: Id42642304b7a06bbabd980c3cb50ddfa26bd349f