Have test_openssl.rb be explicit about security checks it adds

Hey all,

With this commit I'm trying to get JRuby more explicit about the security checks it requires to run. There are three parts to this commit:

1) General framework of being able to set allowed security checks for tests.
2) General security checks that are assumed to be required to get JRuby running (in test/security_helper.rb)
3) Specific security checks required for test_openssl.rb to work.

Please let me know what you think. Assuming this gets merged in, I'd like to tackle test_load.rb next to provide some motivation to get rid of CompoundJar loader. ;)