Now that caches are distinct (https://github.com/travis-ci/travis-ci/issues/4393), we can use the Travis minimal image. The minimal image should take less time to setup and lead to quicker builds.
Also addressed while I'm in here:
- No need to delete the broken google-chrome repo in the minimal image
- Set the hostname to work-around an openjdk bug
- Remove the non-functional apt-cache option
- Remove useless message at completion
- Install jre where the java tests are run
- 'make check' in parallel, since the log will take care of clean output
- 'make check' verbose, so that test failure causes aren't hidden