Several fixes for the bisync integration tests:
- use unique initdir and datadir for each subtest so concurrent tests don't interfere with each other
- remove dots from dir names for bucket backends
- ignore messages specific to cache backend
- skip fix-case tests on backends that can't fix-case
- don't expect "{hashtype} differ" messages on backends with no hash types
- print timestamps in UTC local
More fixes will still be needed, but this should hopefully fix a good portion of them.