Non-caching client

[mengqiy]

We already provide a caching client for controller.

As @pwittrock pointed out, we should provide a no caching client. Because if the cache becomes out-of-date, the admission webhook may make wrong decision based on stale objects. A no-caching client may be helpful in this case.

[mengqiy]

cc: @DirectXMan12 @droot

[DirectXMan12]

it's possible to get a non-caching client, just not easy. We should have a convenience function to make it easy.

[mengqiy]

Another scenario to use a non-caching client is that people may want to avoid having a huge cache locally by using a non-caching client.

[M00nF1sh]

also here: #180

I suggest

1. using manager.GetCache for call that need caching(we can delegate to direct read for unstructured resources)
2. make manager.GetClient always read without caching.

[zjj2wry]

I encountered the same problem when using v0.1.1, the client also gets data from the cache is confusing

https://github.com/kubernetes-sigs/controller-runtime/blob/v0.1.1/pkg/manager/manager.go#L149

[DirectXMan12]

/priority important-longterm

[shawn-hurley]

@DirectXMan12 I think we can close this with #327

[DirectXMan12]

yep!