much moooooore stable release than 2.x :)

Breaking changes

• Remove hhvm role (it didn't work, and php7.x is here to stay so I don't think we need this role anymore)
• Remove ghostscript role (it didn't work since Ubuntu 14.04, and it was only apt-get install ... so it can be replaced by the use of extra_packages variable for instance)
• Elastic products version (such as elasticsearch_version, etc.) no longer accept '*.x' values. The full version number must be provided now (also, default versions have been updated to 5.1.2).

Improvements

• Add elasticsearch-cerebro role (it's here to replace elasticsearch-kopf which doesn't support elasticsearch 5.x).
• Add zsh_plugins and zsh_disable_auto_update variables for oh-my-zsh role (also, symfony2 plugin was added to zsh_plugins by default).
• All variables (except the "deprecated" ones) are now documented.
• Add some configuration variables for Elastic products.

Bug fixes

• Fix apollo role
• Fix elasticsearch role (it was broken on some computers on 5.x versions, because of the default JVM heap size of "2Go"... default value for the heap size is now "512Mo")
• Fix elasticsearch-hq role (it couldn't be provisioned twice+)
• Fix kibana role
• Fix nginx role (default sites.[x].fastcgi_pass configuration was broken if you didn't set php_versions variable)
• Fix rabbitmq role (it was broken if you didn't set rabbitmq variable)
• Fix lua role (typo with luarocks_packages variable)