pytest followup

[TomAugspurger]

Followup issues to #13856

• remove nose entirely (TST: remove nose #15368)
• fix yield base tests, see here. in computation and test_pickle.py, replace with paramterization / fixtures. (TST: Parametrize simple yield tests #15406)
• yield based tests in:
  • frame/test_query_eval.py
  • io/test_packers.py (TST: remove yielding tests from test_msgpacks.py #15427)
  • io/test_pickle.py (TST: convert yield based test_pickle.py to parametrized to remove warnings #15416)
  • test_internals.py (TST: remove rest of yield warnings #15708)
  • test_window.py (TST: remove rest of yield warnings #15708)
• use pytest-dist (Test: use xdist #15369)
• change generator based tests to addopts = --disable-pytest-warnings from setup.cfg (TST: remove rest of yield warnings #15708)
• figure out getlocale failure on travis in pandas/tools/tests/test_util.py:TestLocaleUtils.test_set_locale
• replace @network using pytest.mark (add other markers?)
• fix doc/source/contributing.rst reference to pd.test
• [x] move conftest.py to top-level (TST: move conftest.py to top-level #15731)
• use parametrizeTST: Converting to Pytest Idiom #15990
• use fixtures TST: Converting to Pytest Idiom #15990
• list of skipped tests is failing (TST: print skipped tests files #15408)
• nose.SkipTest -> pytest.skip() (or @pytest.mark.skip or skipif) (TST: remove nose #15368)

[bashtage]

One more candidate: Replace SkipTest with pytest.skip()