Updating Kubernetes tests to properly test missing endpoints code path

[regner]

This fixes #1307

[regner]

As a heads up when I run the provider tests locally I get the following failed test:

--- FAIL: TestDockerLoadDockerServiceConfig (0.00s)
	docker_test.go:3124: expected map[string]*types.Backend{"backend-foo-service":(*types.Backend)(0xc42062cc90)}, got map[string]*types.Backend{"backend-foo":(*types.Backend)(0xc4206576b0)}

This PR doesn't touch anything relating to that test. Curious if it fails in Travis. Haven't looked into why but I am running from head.

[timoreimann]

What's the reason we are able to remove / empty a bunch of server definitions?

[timoreimann]

Oh of course, it's because we now model missingness correctly, right?

[regner]

Yea, see this line: https://github.com/containous/traefik/pull/1436/files#diff-4c0e9bf481017297ab14b697157b2675R2079

[timoreimann]

In my memory, things seemed much more complicated when we tried to do this the first time back on the v1.2 branch. Must have memorized it incorrectly.

LGTM!

[regner]

One of the annoying things was at first I just left the Servers: map[string]types.Server{}, line out, and the tests failed but looked 100% identical according to the output but were actually different.

[timoreimann]

@regner 👍

In the referencing issue, you also mention the fact that we keep frontends dangling when no Endpoints can be found. Do you know what the effect of that is? And should we address it in this PR or a different one? (I'm open to both paths.)

[regner]

I don't know what the effect of that is and am unsure how that should be handled. I think it needs some discussion first so should probably be a different issue and PR.

[timoreimann]

@regner makes sense to me.

[timoreimann]

@regner could you rebase and fix the conflicts? We recently moved all providers into separate sub-packages. Sorry for the inconveniences!