Use appropriate function call for chef 12

[elliott-davis]

In chef12 the function locate_config_file in Chef::Knife was renamed
to chef_config_dir. This patch adds a conditional to check for chef12
and apply the appropriate function call.

[someara]

looks good to me

[jjasghar]

👍

[smurawski]

@jkeiser How's this looking, anything blocking a review?

[jkeiser]

The code itself looks good, but:

• Why are the 1.9.3 tests being removed? We are trying to support the same versions as Chef, and AFAIK we haven't dropped support for it (I could be wrong, happy to be :)
• Is GreenAndSecure included with Chef? It looks like a plugin ... perhaps it's better to use Chef::VERSION so it'll run everywhere.

[elliott-davis]

The problem I was seeing with the 1.9.3 test was:

Gem::InstallError: ohai requires Ruby version >= 2.0.0.

https://github.com/chef/ohai/blob/master/ohai.gemspec#L16

[jkeiser]

OK. Will merge and update travis to not run 1.9.3 anymore. Thanks :)