Add CI job that resyncs CRUD spec tests and runs the test suite

[prashantmital]

This CI job would serve as a leading indicator for when the pymongoexplain API is diverging from PyMogongo's collection API.

Broadly, the job would do the following:

• clone https://github.com/mongodb/specifications
• copy specifications/source/crud/tests/v2/*.json into the corresponding folder in pymongoexplain
• run python setup.py test