Travis and tox config improvements (#28667)

* Use travis_wait only with pylint

pylint is the only job that is expected to be silent for extended time.
For others such a silence is a sign of a problem and using travis_wait
just lengthens the wait, and makes things harder to follow and debug,
because it also suppresses output in the web UI.

* Use pytest-xdist in tox

Similarly as in Azure.

tox.ini

@@ -5,19 +5,21 @@ skip_missing_interpreters = True
 [testenv]
 basepython = {env:PYTHON3_PATH:python3}
 commands =
-     pytest --timeout=9 --durations=10 -qq -o console_output_style=count -p no:sugar {posargs}
+     pytest --timeout=9 --durations=10 -n auto --dist=loadfile -qq -o console_output_style=count -p no:sugar {posargs}
      {toxinidir}/script/check_dirty
 deps =
      -r{toxinidir}/requirements_test_all.txt
      -c{toxinidir}/homeassistant/package_constraints.txt
+     pytest-xdist
 
 [testenv:cov]
 commands =
-     pytest --timeout=9 --durations=10 -qq -o console_output_style=count -p no:sugar --cov --cov-report= {posargs}
+     pytest --timeout=9 --durations=10 -n auto --dist=loadfile -qq -o console_output_style=count -p no:sugar --cov --cov-report= {posargs}
      {toxinidir}/script/check_dirty
 deps =
      -r{toxinidir}/requirements_test_all.txt
      -c{toxinidir}/homeassistant/package_constraints.txt
+     pytest-xdist
 
 [testenv:pylint]
 ignore_errors = True