rewriting the max_clients info gathering using pure ruby ...

and not grep or awk.

I can't change the code in the other PR so decided to issue a new one.

This change will use File.open and regular expressions to gather `apache2[:max_clients]` from `apache2[:config_file]`. I have also changed this to set `apache2[:max_clients]` to "not found" when it can't parse the config value rather than returning nothing as I felt this would be more consistent.

Please let me know what you think.

Cheers
Nico