Migrate to updated Chef debian packages

This PR switches from using apt.opscode.com and its abandoned deb packages in favor of using the latest deb packages from getchef.com.

This upgrades the server to Chef 11, but keeps the clients at Chef 10 - so no recipes have to change - only the setup sequence.  I'm able to successfully bring up a three-node cluster (plus bootstrap node) with this branch.  (Chef does not distribute Debian packages for Chef Server 10...)

Reviews strongly desired.  =)