Add mariadb flavor

The goal of this PR, is to be able to use the libmariadbclient to connect to a mariadb server. To be able to do it, i created a new recipe to install mysql2 gem  instead of mysql one. And by the way i use the mariadb::client recipe (dependency of mysql2_chef_gem::mariadb).

I was unable to compile the mysql gem against the libmariadbclient library.

If you think i need to change something in my way of doing, please tell me :) I do not know if i follow the right way.