Move all output through StatusOutput

Write log output through StatusOutput so that the status implementation
can synchronize it with its own output.

Test: status_test.go
Change-Id: I917bdeeea4759a12b6b4aa6d6d86ee18a2771723

ui/tracer/status.go

@@ -85,3 +85,8 @@ func (s *statusOutput) FinishAction(result status.ActionResult, counts status.Co
 
 func (s *statusOutput) Flush()                                        {}
 func (s *statusOutput) Message(level status.MsgLevel, message string) {}
+
+func (s *statusOutput) Write(p []byte) (int, error) {
+	// Discard writes
+	return len(p), nil
+}