Change how the default route domain is detected on OpenShift

[bbrowning]

The code exposestrategy/route.go attempts to lookup the default domain via getAutoDefaultDomain if one isn't explicitly given and use that to create a hostname for the generated route on OpenShift. This requires cluster-wide admin privileges to do.

Instead of doing this, I propose we pass a blank hostname when creating the RouteSpec if no explicit domain is given and OpenShift will automatically generate one for us that includes the default domain. We can then retrieve the hostname from the generated route for use with addServiceAnnotation. The end result will be the same but this latter method does not require cluster-wide admin privileges.

[jstrachan]

good call - updated to use that mechanism so it uses the spec.host value that gets put onto Routes