Revert "Bump pytest-runner from 5.2 to 6.0.0 in /gremlin-python/src/main/python"
Revert "Bump pytest-runner from 5.2 to 6.0.0 in /gremlin-python/src/main/python"

This reverts commit 9fd2986998efba177120d4c9ed86c73ca6e87033. Upgrade fails in docker for a number of reasons related to the environment tangle that exists in there. Ideally, we would bump the image to bionic, get rid of Python2 stuff, and upgrade to a really fresh version of python. The problem with that is that it will change the testing we do with earlier python version to validate operations which seems like a breaking change as a lot of dependencies need to shift.

apache/tinkerpop,apache/tinkerpop,apache/tinkerpop,apache/tinkerpop,apache/tinkerpop,apache/tinkerpop,apache/tinkerpop