Wait not only until current chef-client is finished,
but also check the running queue of chef clients.

That way we make sure dhcp & PXE config are updated before reboot:
the chef-client run that was supposed to write these settings
might still be in the queue.
Add some comments to explain how we wait for chef-client on state change
Avoid race between chef-client queue getting emptied and chef-client run
Merge pull request #1 from vuntz/race-reinstall

Add some comments to explain how we wait for chef-client on state change
Merge pull request #1164 from jsuchome/wait_for_chef_clients

Wait not only until current chef-client is finished,