[wip] Work around PHPUnit on travis requiring phpenv

Current build errors on travis are caused by an issue in travis and ought to be ignored for now:
https://github.com/travis-ci/travis-ci/issues/2261

This PR *could* work around the changes, but I'm not particularly fond of it.

Travis uses phpenv to configure multiple php versions. We have to run
PHPUnit as root in order to test raw sockets, and phpenv is only
installed / configured for the default user.