mysql_watcher: created a new basic mysql service watcher

[qasimkhan]

This watcher can be used for load balancing

[igor47]

some comments:

• i'm not a fan of shelling out when the task can easily be accomplished by built-in modules. it introduces an unenforceable dependency that's left to the system operator, and is pretty expensive. plus, the way you're shelling out here would reveal some db credentials on the command line
• there are no timeouts enforced here