Adds some build parameters to tune how tests run. There is an example
shown by "gradle helpLocalSettings"
Default C2 off in tests as it is wasteful locally and causes slowdown of
tests runs. You can override this by setting tests.jvmargs for gradle,
or args for ant.
Some crazy lucene stress tests may need to be toned down after the
change, as they may have been doing too many iterations by default...
but this is not a new problem.