Bubble up errors on grpc connections.
Bubble up errors on grpc connections.

The Connect() and Proxy() method always return nil today, as they return
what is received in the stopCh (see [here][link1] and [here][link2]).
When the channel is closed, the nil error is received and then returned.

This patch just changes to send the error (before closing the channel)
when an error was received. This way, we report the proper error to the
grpc layer.

This is mostly a no-op IIUC, but the recommended way in the grpc quick
start.

[link1]: https://github.com/kubernetes-sigs/apiserver-network-proxy/blob/a007c42f6c9d06ff869da5b93c428546658c414e/pkg/server/server.go#L402
[link2]: https://github.com/kubernetes-sigs/apiserver-network-proxy/blob/a007c42f6c9d06ff869da5b93c428546658c414e/pkg/server/server.go#L680

Signed-off-by: Rodrigo Campos <6dfa9cecb562e345739f2e4eb69e9ebd0fbff687@kinvolk.io>

kubernetes-sigs/apiserver-network-proxy