Create log-bin directory if it doesn't exist

It seems the MySQL doesn't like it when you use a log-bin directory that doesn't exist. If you add this before the mysql package is installed then it will fail (if the mysql user doesn't exist). If you add the directory after you run the mysql::server class then mysql will fail to start the first time, it will only be resolved on a subsequent puppet run.
Would using pick() from stdlib be acceptable?
E.g.
```ruby
$logbin = pick($options['mysqld']['log-bin'], $options['mysqld']['log_bin'], '.')
```
Unfortunately pick() won't let me have the third option as undef or ''. It would mean checking for '.' instead of '' or undef