Fix compatibility problem with Chef Client < 11.14.0 

Hi,

I've added a helper method to check if Chef::VERSION is greater or equal than 11.14.0 (where sensitive where introduced). This should bring back the complete Chef 11 compatibility.

I've tested against Ubuntu 14.04, OpenSUSE 13.1 and CentOS 6.5.

What do you think?

Cheers,
Jan