Delete Chef client and node on cleanup

This fixes #1253 by shelling out to `knife` on cleanup, as per
@mitchellh's suggestion in #1255
Show node name in logging
Suppress knife output
Merge branch 'pr/1267'

Conflicts:
	plugins/provisioners/chef/provisioner/chef_client.rb
core: ProvisionerCleanup task to run cleanup on provisioners
core: Inherit CommandUnavailableWindows from CommandUnavailable
provisioners/chef: use Subprocess to execute knife
provisioners/chef: don't delete node/client by default
Update CHANGELOG
provisioners/chef: error if knife not found and auto-deleting
core: better cleanup of ".vagrant"
Update CHANGELOG
provisioners/ansible: execute ansible with cwd of root_path [GH-2051]
commands/up: flag --no-destroy-on-error [GH-2011]
core: set `disabled: true` for disabling forwarded port [GH-1922]