Several improvements

* Run `mysql_upgrade` during MySQL upgrade with `wo stack upgrade` to perform migration if needed
* WordOps now check if a repository already exist before trying to adding it again.
* install script refactored

wo/cli/plugins/stack_migrate.py

@@ -1,7 +1,6 @@
 import configparser
 import os
 
-from cement.core import handler, hook
 from cement.core.controller import CementBaseController, expose
 
 from wo.core.apt_repo import WORepo