Move the Endpoints API test from endpointslice.go to endpoints.go
Move the "kubernetes.default Service exists" and "kubernetes.default
endpoints exist" tests to apiserver.go, since (unlike the rest of
service.go/endpointslice.go) they aren't testing the behavior of the
Service/EndpointSlice/Endpoints APIs.
(No code changes, but fixed a typo in a comment.)
Slightly-more-generic replacement for validateEndpointsPortsOrFail()
(but only validates EndpointSlices, not Endpoints).
Also, add two new unit tests to the Endpoints controller, to assert
the correct Endpoints-generating behavior in the cases formerly
covered by the "should serve endpoints on same port and different
protocols" and "should be updated after adding or deleting ports" e2e
tests (since they are now EndpointSlice-only). (There's not much point
in testing the Endpoints controller in "end to end" tests, since
nothing in a normal cluster ever looks at its output, so there's
really only one "end" anyway.)
kube-proxy does not look at Endpoints ever, so it is incorrect for a
test to assume that there is any correlation between whether Endpoints
exist and whether a Service is working. Tests should only be using the
v1.Endpoints API if they are explicitly testing the behavior of
v1.Endpoints, the Endpoints controller, or the EndpointSlice mirroring
controller. There is no reason for any non SIG Network tests to be
testing any of those things, so there should be no references to
v1.Endpoints in test/e2e outside of test/e2e/network.
Also, simplify some pointlessly complicated e2eservice code.
