e2e: dump stack on ctlTest timeout

Figure out which process is blocking for Elect/Lock test timeouts.

e2e/ctl_v3_test.go

@@ -163,7 +163,7 @@ func testCtl(t *testing.T, testFunc func(ctlCtx), opts ...ctlOption) {
 	}
 	select {
 	case <-time.After(timeout):
-		t.Fatalf("test timed out after %v", timeout)
+		testutil.FatalStack(t, fmt.Sprintf("test timed out after %v", timeout))
 	case <-donec:
 	}
 }