Merge branch 'km/t1400-modernization'

Code clean-up.

* km/t1400-modernization:
t1400: use test_when_finished for cleanup
t1400: remove a set of unused output files
t1400: use test_path_is_* helpers
t1400: set core.logAllRefUpdates in "logged by touch" tests
t1400: rename test descriptions to be unique