Fix flaky TestServer_ReloadInitialUpstreams (#3758)

With the KMS changes this should never have worked at all (because the
different databases means the credentials conveyed after the KMS-based
authentication would never be valid). However, it was sometimes passing
because of a race condition: the worker could be found in the database
before the new credentials were returned to the worker, causing the
worker to start at the KMS step with the second controller.

This changes the test to use the same database for two controllers, but
to only ever have one running at a time, and uses a sequence of two
changed (or unchanged, depending) status updates from the worker to
ensure that the reload was successful.

internal/daemon/controller/testing.go

@@ -810,6 +810,7 @@ func (tc *TestController) AddClusterControllerMember(t testing.TB, opts *TestCon
 		DefaultPassword:                 tc.b.DevPassword,
 		DisableKmsKeyCreation:           true,
 		DisableAuthMethodCreation:       true,
+		DisableAutoStart:                opts.DisableAutoStart,
 		PublicClusterAddr:               opts.PublicClusterAddr,
 		WorkerStatusGracePeriodDuration: opts.WorkerStatusGracePeriodDuration,
 		LivenessTimeToStaleDuration:     opts.LivenessTimeToStaleDuration,