Multiplatform chefspec testing

[shortdudey123]

Partially split from https://github.com/StackStorm/chef-stackstorm/issues/44

Since the cookbook behaves slightly differently on RHEL vs Debian, both sides should be tested in chefspec

Example found in mysql chef cookbook:

• build: https://travis-ci.org/chef-cookbooks/mysql/jobs/172042270
• spec: https://github.com/chef-cookbooks/mysql/blob/master/spec/mysql_server_installation_package_spec.rb