BUG: Seed RNG in test_partially_invalid_plot_data
Came up upon merging another PR. See comment https://github.com/pydata/pandas/pull/6644#issuecomment-38057195

The test relies on drawing at least 1 draw out of 10 uniform draw to be larger than 0.5; even if this didn't cause the failure originally, it should still be fixed. I set a seed that's known to produce the desired values.

gr8! nice to remove the randomness..

I think this might set some global state (which is prob ok), maybe do at the top of the file?
(I think you can also do this in a `with`)
 I didn't see a context manager for the seed, so I defined one in `pandas/utils/testing`.

Do we need a release note? This is mostly internal.
 no release note needed...go ahead when green
 OK. Does anything need to be done on https://github.com/pydata/pandas/pull/6644? Retrigger the build to check that this actually was the bug?

EDIT: I guess this build will include everything from #6644, so it should be OK?
 yep you started with master so if this passes then ok
