Travis: only use Apache as web server

Workaround for build errors with PHP built-in web server since
30-Apr-2014 [1].

[1] https://github.com/travis-ci/travis-ci/issues/2235

Cherry-picked from master.
Conflicts:
	scripts/travis_before_script.sh
Travis before_script add DB_TYPE

Since PHP >= 5.5 has deprecated mysql driver, we use mysqli instead
Travis before script: use PORT variable (align with master)