Various fixes to make travis work with the larger blocktester

Travis needed a number of things, including disabling the new
tests if we're running with DEBUG_LOCKORDER (to prevent timeout),
logging output to a file instead of stderr to avoid running travis
over its max-log limit, disabling the new tests entirely on
Windows (wine), and reducing dbcache for the new tests (to avoid
Travis OOMing us).
TRAVIS: Run dmesg on signal 137 (prints basic OOM kill info)