rust-python-testing: separated base test classes
This will allow, e.g., to change `test-rust-discovery.py` simply
by adding the appropriate base class.
fixbundle() { grep -v 'saving bundle' | grep -v 'saved backup' | \ grep -v added | grep -v adding | \ grep -v "unable to find 'e' for patching" | \ grep -v "e: No such file or directory" | \ cat}