Fix for mysql client installation on non RHEL systems

On Debian based systems the mysql client package is called 'mysql-client'. I tested this change with Ubuntu 12.04 x64. Provision no longer fails.

-----------
```
Error: /Stage[main]/Mysql::Client::Install/Package[mysql_client]/ensure: change from purged to present failed: Execution of '/usr/bin/apt-get -q -y -o DPkg::Options::=--force-confold install mysql' returned 100: Reading package lists...
```