Fix python tests for tornado 5 (#4121)
Fix python tests for tornado 5 (#4121)

* Try with pin and non-api tests

* update appveyor script

* try with tornado 5

* try with tornado 5 and turn back on tests

* revert changes to script

jupyter/jupyterlab,jupyter/jupyterlab,jupyter/jupyterlab,jupyter/jupyterlab,jupyter/jupyterlab