Fixes #6278 : Add additional checks to the installer.

This adds two new checks. One is using the output of java --version
to ensure the version is at least 1.7 and is the OpenJDK. The second
is looking for total available disk space of at least 5 GB. This does
not really ensure a space issue, but it is is a good first cut.
I won't help you much - I think you both are right.

Alternatives is something that javists do use very often. Checking for particular package is perhaps not what we want to do.

Having said that, I bet we will only support Satellite 6 on OpenJDK 1.7 and also we want to give our community working puppet manifests they can use (and improve) standalone. For this reason, you need to also make sure the all required dependencies gets installed.

Therefore I think we should keep both. This extra checker is added value - it errors out early with a clean message. Puppet errors can be tricky to read and we will likely see users with wrong Java stacks installed for sure.

This script is fine, but we need to make sure the dependenci