refs #7264 - check for java, unless installing for capsule

This commit moves the java check from a check to a hook, so that
we can more easily differentiate the behavior for a capsule vs
server install.  In addition, if the installer is being run for
the capsule, skip the java check, since the capsule does not require
it.
@ehelms, it looks like https://github.com/Katello/katello-installer/blob/master/hooks/post/10-post_install.rb#L9 (module_enabled?) might be a reasonable alternative as well.  Going to test with that approach.and will update the PR in the morning when I complete the tests.  Thanks for the feedback.