Bug 1564984

Description of problem:

The problem is related to the way, the `router` works when using `NAMESPACE_LABELS`. When `NAMESPACE_LABELS` are being used for `router` sharding, the `router` applies the following technique to validate and apply a route.

 - The first plugin in this chain is the `HostAdmitter`, which does
   some validation and which is the one that is causing the errors in
   the `router` log as well in the status field of the `route`

 - The second plugin in the chain is the `UniqueHost` plugin, which
   keeps track of which `namespaces` it sees and filters out routes
   that aren't in any of those `namespaces`.

Currently a fix (https://bugzilla.redhat.com/show_bug.cgi?id=1491717) for `HostAdmitter` is in the works, which raises the default log level for the same and thus will avoid the error messages reported on the `router` console.

But that won't solve the problem, as the `route` status is still updated (as before, with the message that validation failed due to the `ALLOWED_DOMAIN` option).

So the problem here is, that `HostAdmitter` is run before `UniqueHost` is run, which is causing all `routes` to be verified by all `routers` and thus reporting back an error if validation is failing.

The good thing is, it does not have any impact on the availability of the platform or it's functionality. Everything is and will continue to work the way expected. The problem is therefore only kind of visualization within the Web-Console and the `route` status.

Problem is, we can't change the Web-Console, as we actually would like to see the `route` status, especially if something is not OK. We therefore want to track the possibility of re-shuffling the `UniqueHost` and `HostAdmitter` plugin if possible to validate the route after selection was applied with `UniqueHost`.

Version-Release number of selected component (if applicable):

 - ose-haproxy-router:v3.6.173.0.96-2

How reproducible:

 - Always

Steps to Reproduce:
1. Setup router sharding as per https://docs.openshift.com/container-platform/3.6/architecture/networking/routes.html#router-sharding and https://docs.openshift.com/container-platform/3.6/install_config/router/default_haproxy_router.html#using-router-shards using `NAMESPACE_LABELS`
2. Configure one `router` with `ALLOWED_DOMAIN`
3. Create a new route for a specific `NAMESPACE_LABELS`
4. Check route status for an error "Rejected by router"

Actual results:

`route` reports "Rejected by router" because it's validation is failing due to `ALLOWED_DOMAIN`

Expected results:

No error to be reported, as validation of `ALLOWED_DOMAIN` should only happen on the `router` the `route` is applied

Additional info:

Issue was discussed with owner of https://bugzilla.redhat.com/show_bug.cgi?id=1491717.