Fix issue where provider doesn't support namespaces

[alexellis]

Expected behaviour

If a provider doesn't support namespaces, then the previous behaviour or a default behaviour should be used

Current behaviour

As outlined by @bmcstdio, the code will throw a fatal error instead.

https://github.com/openfaas-incubator/connector-sdk/blob/master/types/controller.go#L156-L159

Possible solution

• Handle a 404 error gracefully
• Retain existing fatal error behaviour for any other status code
• Update unit tests

Context

faas-netes is unaffected, but users wanting to bring in the latest release of the connector-sdk will encounter issues when used with the operator or faas-swarm.

[alexellis]

cc: @bmcstdio @viveksyngh @LucasRoesler