ipn/ipnlocal,control/controlclient: make Logout more sync

We already removed the async API, make it more sync and remove
the FinishLogout state too.

This also makes the callback be synchronous again as the previous
attempt was trying to work around the logout callback resulting
in a client shutdown getting blocked forever.

Updates #3833

Signed-off-by: Maisem Ali <maisem@tailscale.com>

tstest/integration/integration_test.go

@@ -945,9 +945,11 @@ func (n *testNode) StartDaemonAsIPNGOOS(ipnGOOS string) *Daemon {
 
 func (n *testNode) MustUp(extraArgs ...string) {
 	t := n.env.t
+	t.Helper()
 	args := []string{
 		"up",
 		"--login-server=" + n.env.ControlServer.URL,
+		"--reset",
 	}
 	args = append(args, extraArgs...)
 	cmd := n.Tailscale(args...)