Inject /etc/hhvm/php.ini in PHP's configure for HHVM

We need to run this before paranoid_mode disables sudo

This fixes https://github.com/travis-ci/travis-ci/issues/2863 and
https://github.com/travis-ci/travis-ci/issues/2523.
Pleasing @meatballhat
Merge pull request #322 from travis-ci/ha-bug-hhvm-ini-fixes

Inject /etc/hhvm/php.ini in PHP's configure for HHVM