This is the beginning of a validating admission controller which we will
use to permit end-users access to manage Ingresses.
This first pass implements an ingressFilter, which is the main structure
through which allowed namespace/dns combinations will be allowed. The
interface is currently via a test, but in the future this will likely be
configured via a command line, or via a serialized protobuf config.
Change-Id: I22dbed633ea8d8e1fa02c2a1598f37f02ea1b309
q3k