Fix the JRuby tests that skip/fail for no good reason

[nateberkopec]

The only tests we should be skipping on JRuby are the ones where the feature isn't supported by the platform. I had to add a bunch of skips to get us back to green (skip_on). We should remove these test-by-test.

I'm 99% confident that the problem in all these cases is just racy tests rather than code, but the only way to be sure is a passing test.

[dentarg]

Related issue about JRuby build failures (back when tests ran on Travis CI): #1982

[dentarg]

Here are the recent commits that skipped tests for JRuby: 00e20d8...e42d3a6