Pull in more -dev packages to get more modules building (including mod_md). Test gcc 7 on bionic, xenial is the Travis default anyway. Only add the toolchain PPA where really needed.
Update travis config
* Add 'if TRAVIS_OS_NAME' to before_install/before_script/script to allow multi-os testing. * Add separation lines in matrix config (better visual impact). * Add Linux to all the current job's name. * Add tests for Worker mpm.
Move before/run scripts out of .travis.yml.
Reviewed by: elukey
Support 2.4.x builds, which lacks --with-test-suite support. Build with --enable-load-all-modules only when the test suite is run.
Add Travis support for multiple APR/APR-util versions. Add an APR build with --enable-pool-debug.