message: Initialize the dbcache size and nCoinCacheMaxSize for the unit tests
  In test_bitcoin.cpp initialize these values. This prevents us from
  accidentally using up RAM during unit tests runs and also fixes
  a bug in the txvalidationcache tests which was preventing us from
  flushing the dbcache at the start of the test run.
diff: @@ -73,6 +73,13 @@ TestingSetup::TestingSetup(const std::string &chainName) : BasicTestingSetup(cha
  bool worked = InitBlockIndex(chainparams);
  assert(worked);
  + // Initial dbcache settings so that the automatic cache setting don't kick in and allow
  + // us to accidentally use up our RAM on Travis, and also so that we are not prevented from flushing the
  + // dbcache if the need arises in the unit tests (dbcache must be less than the DEFAULT_HIGH_PERF_MEM_CUTOFF
  + // to allow all cache entries to be flushed).
  + SoftSetArg("-dbcache", std::to_string(5));
  + nCoinCacheMaxSize.store(5000000);
  +
  // Make sure there are 3 script check threads running for each queue
  SoftSetArg("-par", std::to_string(3));
  PV.reset(new CParallelValidation());
  