test-fuse: format save name with python, not bash

test-fuse: format save name with python, not bash

Some versions of bash don't support the date expansion we used.

Thanks to pspdevel for reporting the issue.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Tested-by: Rob Browning <rlb@defaultvalue.org>
Reviewed-by: Gabriel Filion <gabster@lelutin.ca>
Tested-by: Gabriel Filion <gabster@lelutin.ca>
[rlb@defaultvalue.org: add comment above savename()]
Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Tested-by: Rob Browning <rlb@defaultvalue.org>