Moving away from RNG bases in testing

[pc494]

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name: Moving away from RNG bases in testing
about: We used to test that any random basis gives a change, now we use a specific one.

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Release Notes

developer change
Summary: n/a

What does this PR do? Please describe and/or link to an open issue.
#458 is currently failing on a Random Number Generator test, in this case
a) the RNG doesn't actually aid us in testing the functionality
b) Debugging it isn't really possible

So I've removed the random element in the failing test.

[coveralls]

Coverage remained the same at 100.0% when pulling f788975 on pc494:bugfix-rng-in-tests into fed6233 on pyxem:master.

[pc494]

This does what it was meant to; but as noted in #461 the appveyor is upset about something unrelated to these PR's

[dnjohnstone]

Good change, do you have any idea what the appveyor issue is about? I know it's not this, but I also don't know what it is...