OmeroPy: Update methods in path.py to wrap os.path properly

Merge the changes from
https://github.com/jaraco/path.py/commit/bee13d0de4d44599d397b603e1c83dce1ce9818d
Revert "python: Use os.path.isdir(p) rather than p.isdir()"

This reverts commit 2ee95fa1d3f800c3ad16069c051c12b9a750b8e1.