[COOK-3091] Check that Chef::Config[:config_file] exists before reading
[COOK-3091] Check that Chef::Config[:config_file] exists before reading

Signed-off-by: Seth Vargo <81550dbf04dfd8537ff7b3c014c6fbf86e0889dc@gmail.com>

kplimack/ohai,RelateIQ-chef/ohai-cookbook,Altiscale/ohai,mevic/ohai,signe/ohai,predominant/ohai,chef-cookbooks/ohai,opscode-cookbooks/ohai,scalp42/ohai,higanworks-cookbooks/ohai,7bfa689ac3c4be50f8ba6c1ea8c5f316/ohai,protec-cookbooks/ohai