Merge pull request #2267 from Unity-Technologies/develop-enforce-coverage

Enforce min coverage percentage

.gitignore

 .DS_Store
 .ipynb_checkpoints
 
-# pytest cache 
+# pytest cache
 *.pytest_cache/
 
 # Ignore compiled protobuf files.
 # Python virtual environment
 venv/
 .mypy_cache/
+
+# Code coverage report
+.coverage

setup.cfg

+[coverage:report]
+# Run "pytest --cov=mlagents" to see the current coverage percentage.
+# Run "pytest --cov=mlagents --cov-report html" to get a nice visualization of what is/isn't coverge in html format.
+fail_under = 60