Pin to pytest<=3.0.7 pytest-xdist<=1.16.0
Pin to pytest<=3.0.7 pytest-xdist<=1.16.0

Until https://github.com/pytest-dev/pytest-xdist/issues/196 is fixed

Change-Id: I35004dd8bea240b7d91d72f2ea86cb732fe861e0

zzzeek/alembic,sqlalchemy/alembic