Runlist conflicts with policy_name and policy_group settings in first-boot.json

When a runlist isn't specified and policy_name and policy_group settings are added to the custom json attributes like so:

"custom_json_attr": {
            "policy_group": "[parameters('chefPolicyGroup')]",
            "policy_name": "[parameters('chefPolicyName')]"
          }

an empty run list is still added to the first-boot.json file. These settings conflict causing the first converge to fail. The resolution would be to not write a run_list into the first-boot.json file at all if the runlist is not provided.

This, for a linux host, appears to happen here:

azure-chef-extension/lib/chef/azure/commands/enable.rb

Line 220 in bccc0cf

runlist = @run_list.empty? ? [] : escape_runlist(@run_list)

This should be fixed by #213 in version 1210.12.109.1004 of the extension.