Fix nsupdate plugin config bind key name

This fixes the nsupdate plugin config to work when bind key is not
the same as the domain name.

This was driving me crazy trying to work out why dynamic updates
weren't working when used with an existing DNS infrastructure.
Merge pull request #157 from danehans/cartridge_install

Fixes Cartridge Installations
Merge remote-tracking branch 'upstream/pr/139' into PRtest

Conflicts:
	README.asciidoc
	manifests/init.pp