Security recommendations may be more restrictive #76
Description
The requirements on security purpose (in readme.md) are much more open than needed.
- Specify the scope for each right (maybe only on mysql.*) would be great
- As some checks (metrics-mysql-raw.rb) use only the request show global variables, select is not needed (according to https://dev.mysql.com/doc/refman/5.6/en/show-variables.html)