remove testing debug logs from matplotlib

[erohmensing]

While using rasa test --debug to look into how the testing predictions are made, we get lots of annoying debug messages from matplotlib which fill up the console logs:

2020-10-05 12:09:35 DEBUG    matplotlib.font_manager  - findfont: score(<Font '.SF NS Text Condensed' (SFNSTextCondensed-Semibold.otf) normal normal semibold condensed>) = 10.44
2020-10-05 12:09:35 DEBUG    matplotlib.font_manager  - findfont: score(<Font 'AppleGothic' (AppleGothic.ttf) normal normal regular normal>) = 10.05
2020-10-05 12:09:35 DEBUG    matplotlib.font_manager  - findfont: score(<Font 'STIXNonUnicode' (STIXNonUniIta.otf) italic normal 400 normal>) = 11.05
2020-10-05 12:09:35 DEBUG    matplotlib.font_manager  - findfont: score(<Font 'STIXIntegralsSm' (STIXIntSmReg.otf) normal normal regular normal>) = 10.05
2020-10-05 12:09:35 DEBUG    matplotlib.font_manager  - findfont: score(<Font '.SF Compact Rounded' (SFCompactRounded-Ultralight.otf) normal normal ultralight normal>) = 10.335
2020-10-05 12:09:35 DEBUG    matplotlib.font_manager  - findfont: score(<Font 'Times New Roman' (Times New Roman Bold Italic.ttf) italic normal roman normal>) = 11.145
2020-10-05 12:09:35 DEBUG    matplotlib.font_manager  - findfont: score(<Font 'Papyrus' (Papyrus.ttc) normal normal 400 condensed>) = 10.25
2020-10-05 12:09:35 DEBUG    matplotlib.font_manager  - findfont: score(<Font 'STIXSizeOneSym' (STIXSizOneSymReg.otf) normal normal regular normal>) = 10.05

and

2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - vmin 1.0 vmax 4.0
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - ticklocs array([  0.1,   1. ,  10. , 100. ])
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - vmin 1.0 vmax 4.0
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - ticklocs array([  0.1,   1. ,  10. , 100. ])
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - vmin 1.0 vmax 4.0
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - ticklocs array([2.e-01, 3.e-01, 4.e-01, 5.e-01, 6.e-01, 7.e-01, 8.e-01, 9.e-01,
       2.e+00, 3.e+00, 4.e+00, 5.e+00, 6.e+00, 7.e+00, 8.e+00, 9.e+00,
       2.e+01, 3.e+01, 4.e+01, 5.e+01, 6.e+01, 7.e+01, 8.e+01, 9.e+01,
       2.e+02, 3.e+02, 4.e+02, 5.e+02, 6.e+02, 7.e+02, 8.e+02, 9.e+02])
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - vmin 1.0 vmax 4.0
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - ticklocs array([  0.1,   1. ,  10. , 100. ])
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - vmin 1.0 vmax 4.0
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - ticklocs array([  0.1,   1. ,  10. , 100. ])
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - vmin 1.0 vmax 4.0
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - ticklocs array([2.e-01, 3.e-01, 4.e-01, 5.e-01, 6.e-01, 7.e-01, 8.e-01, 9.e-01,
       2.e+00, 3.e+00, 4.e+00, 5.e+00, 6.e+00, 7.e+00, 8.e+00, 9.e+00,
       2.e+01, 3.e+01, 4.e+01, 5.e+01, 6.e+01, 7.e+01, 8.e+01, 9.e+01,
       2.e+02, 3.e+02, 4.e+02, 5.e+02, 6.e+02, 7.e+02, 8.e+02, 9.e+02])
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - vmin 1.0 vmax 4.0
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - ticklocs array([  0.1,   1. ,  10. , 100. ])
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - vmin 1.0 vmax 4.0
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - ticklocs array([  0.1,   1. ,  10. , 100. ])
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - vmin 1.0 vmax 4.0
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - ticklocs array([2.e-01, 3.e-01, 4.e-01, 5.e-01, 6.e-01, 7.e-01, 8.e-01, 9.e-01,
       2.e+00, 3.e+00, 4.e+00, 5.e+00, 6.e+00, 7.e+00, 8.e+00, 9.e+00,
       2.e+01, 3.e+01, 4.e+01, 5.e+01, 6.e+01, 7.e+01, 8.e+01, 9.e+01,
       2.e+02, 3.e+02, 4.e+02, 5.e+02, 6.e+02, 7.e+02, 8.e+02, 9.e+02])
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - vmin 1.0 vmax 4.0
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - ticklocs array([  0.1,   1. ,  10. , 100. ])
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - vmin 1.0 vmax 4.0
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - ticklocs array([  0.1,   1. ,  10. , 100. ])
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - vmin 1.0 vmax 4.0
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - ticklocs array([2.e-01, 3.e-01, 4.e-01, 5.e-01, 6.e-01, 7.e-01, 8.e-01, 9.e-01,
       2.e+00, 3.e+00, 4.e+00, 5.e+00, 6.e+00, 7.e+00, 8.e+00, 9.e+00,
       2.e+01, 3.e+01, 4.e+01, 5.e+01, 6.e+01, 7.e+01, 8.e+01, 9.e+01,
       2.e+02, 3.e+02, 4.e+02, 5.e+02, 6.e+02, 7.e+02, 8.e+02, 9.e+02])
2020-10-05 12:09:35 DEBUG    matplotlib.ticker  - vmin 1.0 vmax 4.0

[erohmensing]

closed in #6902