Restrict faasd to labelled namespaces only

Changelog for 0.14.2:

• PR #204 Add check for namespace label openfaas=true by @Waterdrips

Commits
3fe0d8d Update messages to want/got for unit tests by @alexellis
5aa4c69 Inline namespace check and create const for label by @alexellis
12b5e8c Add check for namespace label openfaas=true by @Waterdrips

Generated by Derek