(MODULES-552) Add capability to specify column_privileges

Fixes Jira Issue [MODULES-552](https://tickets.puppetlabs.com/browse/MODULES-552).
The PROXY privilege must be named by itself, so while this test passes, applying it in a manifest doesn't work:

```
Error: Execution of '/usr/bin/mysql -e GRANT PROXY, SELECT (a, b) ON *.* TO 'nss-user'@'%' WITH GRANT OPTION' returned 1: ERROR 1064 (42000) at line 1: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'PROXY, SELECT (a, b) ON *.* TO 'nss-user'@'%' WITH GRANT OPTION' at line 1
```

Could you change the test to have privileges `['SELECT(Host,Address)', 'INSERT']` or something similar just so it's not misleading?