Allow building Cassandra with Java 11 Support

[rustyrazorblade]

Currently the build process only uses Java 8 for builds, which won't be a good long term solution. Cassandra 4 can work with Java 11, although it's experimental right now.

We should probably pull Java 11 into the docker image and use update-java-alternatives to pick the compile version. I'm thinking we'll need to set a flag to decide what to build, but I'm open to discuss this as I don't have a strong opinion on the best approach.

We'll need to also update the install scripts to install java 11 in addition to 8, and most likely use the same update-java-alternatives.

I think for the install it wouldn't be particularly inconvenient to add an extras/ directory under provisioning/cassandra/ that could install java 11 and set it to the default, if you want it you just copy the script into provisioning/cassandra.

[rustyrazorblade]

@rzvoncek any interest in working on this?

[rzvoncek]

@rustyrazorblade, yeah, I'd like to give it a shot.