Review use of numpy array print formats, and Python2/3 variation

[pp-mo]

Iris tests need a stable array print format when comparing text results:

• in doctests, and
• within assertCML testing.

This caused considerable difficulties when adding Matplotlib 2 support.
See : #3019 (comment)

Recently this happens again, since numpy 1.15 (?probably).
We now have different printouts in Python 2 and Python 3.
See : #3134
N.B. I think this does not relate to use of the 'legacy' option, As this only has effect in printing Iris objects. Whereas, the docstring incompatibility encountered in #3134, e.g. between travis test 8514.7 and 8514.8 here, happens when just printing arrays.

TODO:

• see if there is anything better we can do here
• see if this is a mistake in numpy, or if they just don't care about this kind of difference

[rcomer]

I'm not sure if this issue is still relevant as it mentions python 2. If it is still relevant, would use of numpy.set_printoptions help?

[pp-mo]

I think this was actually addressed, in much the way you suggest.
So I judge this was not just not linked and should have been closed.

Thanks for looking!
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