RFE - add debugging info for ByteMutation and other MLVM vm testbase tests

Modify the vm testbase class, vm.mlvm.anonloader.share.StressClassLoadingTest, to save the mutated class file when the JVM crashes while running the ByteMutation test or other tests that use the StressClassLoadingTest class.

Also, provide a mechanism for specifying a specific non-random seed when trying to reproduce nightly test failures involving tests that use vm testbase class vm.mlvm.share.Env.