Implementation of the handshake protocol in https://github.com/mongodb/motor/commit/2024c7c97c9ef8860c22df7ba1ae55b77b23b298 has rendered MOTOR unusable with PyMongo 3.6 because the DriverInfo API was only added to PyMongo 3.7 onwards (see https://github.com/mongodb/mongo-python-driver/commit/c63c068611bd4ea3387fc1a08082a96869ac82a1).

This is problematic because the current setup.py asserts that install_requires = ['pymongo>=3.6,<4'] so users can easily end up with an environment that is non-operational.

Example of the failure (packages were pip-installed in a clean virtualenv with pymongo-3.6.0 being installed first):

$ pip list
Package    Version
---------- -------
motor      2.0.0
pip        19.1.1
pymongo    3.6.0
setuptools 41.0.1
wheel      0.33.4
$ python -c "import motor.core"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/Users/pmital/Developer/motor/motor/core.py", line 37, in <module>
    from pymongo.driver_info import DriverInfo
ModuleNotFoundError: No module named 'pymongo.driver_info'