CHEF-4443 - Always save the correct run list

As per Dan's suggestions, use a primary run_list and an override, and
take care to ensure that the correct one is used to save the node.
add run_list setter
Merge remote-tracking branch 'origin/master' into save-right-run-list

Conflicts:
	lib/chef/client.rb
move run_list twiddling into the policy builder
Merge pull request #948 from thommay/chef-4443

CHEF-4443 - Always save the correct run list