test_time failure in CI logs
The following failure has shown up a couple times in CI today. Haven't looked in detail but assume it to be an unreliable test.

https://dev.azure.com/pandas-dev/pandas/_build/results?buildId=9836&view=logs&jobId=a69e7846-138e-5465-0656-921e8964615b&taskId=56da51de-fd5a-5466-5244-b5f65d252624&lineStart=42&lineEnd=95&colStart=1&colEnd=64

```
=================================== FAILURES ===================================
_____________________________ TestTSPlot.test_time _____________________________
[gw0] linux -- Python 3.6.6 /home/vsts/miniconda3/envs/pandas-dev/bin/python

self = <pandas.tests.plotting.test_datetimelike.TestTSPlot object at 0x7f2889f69978>

    @pytest.mark.slow
    def test_time(self):
        t = datetime(1, 1, 1, 3, 30, 0)
        deltas = np.random.randint(1, 20, 3).cumsum()
        ts = np.array([(t + timedelta(minutes=int(x))).time() for x in deltas])
        df = DataFrame({'a': np.random.randn(len(ts)),
                        'b': np.random.randn(len(ts))},
                       index=ts)
        fig, ax = self.plt.subplots()
        df.plot(ax=ax)
    
        # verify tick labels
        fig.canvas.draw()
        ticks = ax.get_xticks()
        labels = ax.get_xticklabels()
        for t, l in zip(ticks, labels):
            m, s = divmod(int(t), 60)
            h, m = divmod(m, 60)
            rs = l.get_text()
            if len(rs) > 0:
                if s != 0:
                    xp = time(h, m, s).strftime('%H:%M:%S')
                else:
                    xp = time(h, m, s).strftime('%H:%M')
                assert xp == rs
    
        # change xlim
        ax.set_xlim('1:30', '5:00')
    
        # check tick labels again
        fig.canvas.draw()
        ticks = ax.get_xticks()
        labels = ax.get_xticklabels()
        for t, l in zip(ticks, labels):
            m, s = divmod(int(t), 60)
            h, m = divmod(m, 60)
            rs = l.get_text()
            if len(rs) > 0:
                if s != 0:
                    xp = time(h, m, s).strftime('%H:%M:%S')
                else:
                    xp = time(h, m, s).strftime('%H:%M')
>               assert xp == rs
E               AssertionError: assert '01:06:40' == '03:40'
E                 - 01:06:40
E                 + 03:40
```