Travis CI: Update HHVM

[netweb]

HHVM 3.6.x LTS is ​no longer supported, end of support was 1 March 2016

Travis CI "Legacy" infrastructure uses Ubuntu 12.x "Precise" and is limited to the last HHVM version supported by Facebook for Ubuntu 12.x Precise HHVM version 3.6.6

Facebook's HHVM LTS support of Ubuntu 12.x Precise and HHVM v3.6.x ended 1 March 2016.

Updating the HHVM job to Travis CI's "Trusty beta build environment" will allow us to use the latest HHVM versions currently at v3.13.1 on Ubuntu 14.x "Trusty"

[ocean90]

From ​https://docs.travis-ci.com/user/trusty-ci-environment/#PHP

Note: We’re unable to build PHP 5.2 on Trusty so far, so trying to use it will result in a build failure when phpenv fails to compile it

[netweb]

Replying to ocean90:

From ​https://docs.travis-ci.com/user/trusty-ci-environment/#PHP

Note: We’re unable to build PHP 5.2 on Trusty so far, so trying to use it will result in a build failure when phpenv fails to compile it

Yes, I found out jobs can be mixed across environments, I plan on using Trusty for HHVM, PHP 5.2 will remain on Precise

[netweb]

Patch 36930.1.diff​ is the same as this pull request: ​https://github.com/aaronjorbin/develop.wordpress/pull/4

Travis CI Build via above pull request: ​https://travis-ci.org/aaronjorbin/develop.wordpress/builds/132724396
Ubuntu 14.04 Trusty - HHVM 3.13.1 - MySQL 5.6: ​https://travis-ci.org/aaronjorbin/develop.wordpress/jobs/132724404

The patch also has a few other tweaks for Travis CI:

• It uses MySQL 5.6 for the HHVM job as the default MySQL 5.5 does not currently work on the Trusty environment

• Adds installed apt packages to the cache, in this case MySQL 5.6 for the HHVM job

• The per job environment variable WP_TRAVISCI=travis:phpunit is now set globally rather than per job, and overridden as needed, i.e. the "grunt build"/"javascript" .1 job using WP_TRAVISCI=travis:js

• The MySQL user is changed from travis to root, either works on the legacy environment but only root works on the Trusty environment

• A couple of debug lines to echo per job the version of PHP & MySQL being used to aid in easily debugging Travis CI build environment issues

[pento]

In 37555:

Tests: Upgrade the HHVM job to use Ubuntu Trusty, and a more recent version of HHVM.

Also includes some tidying up of the .travis.yml file.

Props netweb.

Fixes #36930.