Add posargs (#324)

Fixes #323

Author: ocelotl

tox.ini

@@ -88,7 +88,7 @@ commands_pre =
   mypyinstalled: pip install file://{toxinidir}/opentelemetry-api/
 
 commands =
-  test: pytest
+  test: pytest {posargs}
   coverage: {toxinidir}/scripts/coverage.sh
 
   mypy: mypy --namespace-packages opentelemetry-api/src/opentelemetry/