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.
The line I linked you verifies installed and/or installs if not found. What I mean is, I feel like it should be up to the individual services to set and ensure the Java version needed and for the installer to be not have to be directly aware of the dependencies of the services.