bugfix for view.py numInvIfgram.py for hyp3 products

[yunjunz]

Description of proposed changes

• ifgram_inversion: ignore the NO_DATA_VALUE metadata from the hyp3 ifgram stack file, while creating the # of inverted ifgram file, because 1) the zero value is valid (not no-data-value), and 2) to avoid the strange plotting error from matplotlib. The detailed reason seems to be within matplotlib, not within mintpy code itself.

• tests/configs/RidgecrestSenDT71: turn back ON the plotting during testing.

Reminders

• Fix view.py numInvIfgram.h5 error for RidgecrestSenDT71 #1185
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• Pass Codacy code review (green)
• Pass Circle CI and local tests (green)
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[forrestfwilliams]

Thanks for this @yunjunz!

[yunjunz]

I think the code is now for a new release, will try to do it in the coming few days. Cheers!