Disable centos 6 testing for now
Disable centos 6 testing for now

Current chef release handles fqdn detection in travis just fine, but
chef 12.3 in the omnibus package doesn't.

Signed-off-by: Tim Smith <764ef62106582a09ed09dfa0b6bff7c05fd7d1e4@chef.io>

irvingpop/supermarket-omnibus-cookbook,GannettDigital/chef-supermarket-omnibus-cookbook,chef-cookbooks/supermarket-omnibus-cookbook,nellshamrell/supermarket-omnibus-cookbook