feat(core): add namespace provider

[zachsmith1]

The new NamespaceProvider will support querying accounts for namespaces, spaces, etc. There are places across spinnaker, like Deck, that need this information to populate fields for users. Before this change, this data is gathered by calling the /credentials endpoint and then parsing the namespaces/etc from that account. It doesn't make sense to continue to parse this information from a credentials object directly. Allowing this data to be fetched independently allows for better scalability and control.

[spinnakerbot]

The following commits need their title changed:

• cf31437: Merge pull request restrict load balancer lookup to application name #1 from spinnaker/master

• b7c2f79: Merge pull request Kato clouddriver rebase #2 from spinnaker/master

• 5bdc220: update master

• a242c8d: Merge pull request Clouddriver kato 20150629 #4 from spinnaker/master

• 6149626: Merge pull request Clouddriver oort 20150629 #5 from spinnaker/master

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[ncknt]

We're using the term region in many places (coming from AWS), location in others. I'm hesitant to add one more term. I think it only matches Kubernetes (?)

[zachsmith1]

Yes, Namespace in its literal sense is a k8 object but the abstraction is more or less what I was trying to accomplish. Namespace being a logical grouping around some resource. This happens to be a 1-1 with k8 and very close to 1-1 with CF (Org + Space combo). These are also dynamic in nature and can be created/updated/deleted. The tight coupling between the credentials and these "namespaces" is the main reason for this PR. Regions being more static might not make sense in this light

I'm open to calling it something different if you have a better abstraction in mind?

[ncknt]

I was thinking location to be consistent. It's not a very strongly held feeling on my side, I just wanted you to be aware that it's yet another naming scheme. Alternative idea: we could define: /credentials/kubernetes/[account name]/namespaces for Kubernetes, /credentials/cloudfoundry/[account name]/spaces for CF, etc. I guess it depends how you plan to use this in Deck.