batou.lib.mysql.Grant: Only appending

[frlan]

This might be a tricky problem, when it comes to the details. However: batou.lib.mysql.Grant at the moment only appends new GRANTS to the current ones. If e.g. something like this was used some time:

self += batou.lib.mysql.Grant(
            "*",
            user=susername,
            admin_password=admin_password,
            allow_from_hostname="%")

the GRANT is not cleaned up after changing this statement.

[ctheune]

This smells like a good specific use case for #364 ! :)