Fix Flaky TestProcessKubeCSR

[jimbishopp]

The TestProcessKubeCSR test in lib/auth fails intermittently due to the Kubernetes feature being disabled. The test expects a NotFound error but receives an invalid license error instead. Usually other tests enable the Kubernetes feature before this test runs, but occasionally the test executes without Kubernetes and fails.

This change explicitly enables the Kubernetes feature by generalizing a pattern for setting module features used by the TestDesktopAccessDisabled test.

The following is the location where the test failed and the output received.

_, err = s.a.ProcessKubeCSR(csr)
require.Error(t, err)
require.True(t, trace.IsNotFound(err), "got: %v", err) // failure

=== CONT  TestProcessKubeCSR
kube_test.go:69: 
  Error Trace:	kube_test.go:69
  Error:      	Should be true
  Test:       	TestProcessKubeCSR
  Messages:   	got: this Teleport cluster is not licensed for Kubernetes, please contact the cluster administrator

Flaky Test Tracker: #9492

[zmb3]

Global state strikes again.

[zmb3]

@jimbishopp do we need to do this in more places? A quick search for SetModules uncovers uses in hsm_test.go, tls_test.go, keystore_test.go, and a bunch more..

[jimbishopp]

@zmb3 Yeah, we probably should. I'll find the others and update them in a new PR.