(#21321) Disable support for SSLv2Hello protocol

By default, the JVM allows for SSLv2 client "hello" messages for all
secure sockets. Note that this isn't the full SSLv2 protocol, but rather
just a backwards-compatible "hello" message:

http://tools.ietf.org/html/rfc4346#appendix-E

Still, the general recommendation is to disable use of that.