Add travis, appveyor and codecov passenvs

Some of these environment variables are necessary codecov to
detect that it is on travis/appveyor and thus doesn't need
an upload token.

tox.ini

@@ -7,7 +7,7 @@
 [testenv]
 deps=-rtests/requirements.txt
 setenv=COVERAGE_FILE={toxworkdir}/.coverage.{envname}
-passenv=APPDATA USERPROFILE HOMEDRIVE HOMEPATH windir APPVEYOR
+passenv=APPDATA USERPROFILE HOMEDRIVE HOMEPATH windir APPVEYOR APPVEYOR_* CI CODECOV_* TRAVIS TRAVIS_*
 # These are separate so xfail tests don't count towards code coverage
 commands=pytest -m "not xfail" {posargs: "{toxinidir}" --cov-config={toxinidir}/tox.ini --cov=setuptools}
          pytest -m "xfail"  {posargs: "{toxinidir}"}