fix the problems with random seeds in tests.

[segasai]

previously tests influenced each other. Now each script has its own seed set up by pytest.fixture.

[joshspeagle]

Should I plan to review and accept both this and #248 then?

[segasai]

This patch is non-controversial, ready to be reviewed and committed. The #248 needs a careful separate look/review. I am not 100% certain in its correctness. But #248 is ready for review too

[coveralls]

Pull Request Test Coverage Report for Build 854323841

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.02%) to 71.886%

---

Files with Coverage Reduction	New Missed Lines	%
py/dynesty/utils.py	1	41.47%
<!--	Total:	1		-->

Totals
Change from base Build 839449013:	-0.02%
Covered Lines:	3365
Relevant Lines:	4681

---

💛 - Coveralls