BUG: Fixes #9281: fixes to tseries.tests.test_tslib.TestTimestamp

[Garrett-R]

closes #9281

The last test of both test_now and test_today was passing for anyone with a timezone
of UTC-5 or greater (but failed, for example, in US/Pacific). The test was not
testing what the original author meant it to (which is that the times are very close
together) so I added abs(.) around the Timedeltas and also fixed the errant test.

[jreback]

thanks!

[rockg]

I don't think abs() is necessary here given the order that the times are created so the difference will always be positive. Nevertheless, thanks for fixing.

[Garrett-R]

@rockg, yeah, I wasn't too sure about the abs, but I was thinking it makes the tests more likely to catch some problematic code that someone writes in the future. For example, take

self.assertTrue(abs(ts_from_method_tz - ts_from_string_tz) < delta)

If someone ends up rewriting Timestamp.now(tz='US/Eastern') and it erronesously causes ts_from_string_tz to have a value corresponding to the user's local time instead of US/Eastern, then because of abs, the test will fail not only for users with a timezone less than UTC-5, but rather for everyone.