timer callback plugin: handle timezone changes better

A playbook that does `timezone name=Australia/Brisbane` on
a host previously in UTC will appear to take 10 hours.

Improve the seconds handling for playbooks that take longer
than one hour.
Improve the hours handling for playbooks that take longer than
one day.

TZ change before:
```
Playbook run took 0 days, 10 hours, 0 minutes, 36055 seconds
```
After:
```
Playbook run took 0 days, 0 hours, 0 minutes, 55 seconds
```

Sleep for 100s more than one hour before:
```
Playbook run took 0 days, 1 hours, 1 minutes, 3641 seconds
```

After:
```
Playbook run took 0 days, 1 hours, 1 minutes, 41 seconds
```

lib/ansible/plugins/callback/timer.py

@@ -20,17 +20,17 @@ class CallbackModule(CallbackBase):
 
         super(CallbackModule, self).__init__()
 
-        self.start_time = datetime.now()
+        self.start_time = datetime.utcnow()
 
     def days_hours_minutes_seconds(self, runtime):
         minutes = (runtime.seconds // 60) % 60
-        r_seconds = runtime.seconds - (minutes * 60)
+        r_seconds = runtime.seconds % 60
         return runtime.days, runtime.seconds // 3600, minutes, r_seconds
 
     def playbook_on_stats(self, stats):
         self.v2_playbook_on_stats(stats)
 
     def v2_playbook_on_stats(self, stats):
-        end_time = datetime.now()
+        end_time = datetime.utcnow()
         runtime = end_time - self.start_time
         self._display.display("Playbook run took %s days, %s hours, %s minutes, %s seconds" % (self.days_hours_minutes_seconds(runtime)))