Adapt cookbooks for the Bluebox environment
Allow setting up multiple deployments of the worker.

Bump cookbook version too.
Fix hostname.
Add support for GNU Multiple Precision (GMP) PHP extension.

The extension is not available for PHP 5.2 because it does not support
latest libgmp versions.

Fixes #141.
Enable Zend Thread Safety for PHP.

Fixes travis-ci/travis-ci#917.