Previously, the mandatory location, directory and branch positional
arguments were passed as part of the varargs. This meant the varargs
were conflating flags and positional arguments, making it harder to add
new positional arguments.
Move the mandatory positional arguments to separate parameters for
do_export(). This introduces no functional changes, but makes later
commits easier.
Signed-off-by: Philip Withnall <withnall@endlessm.com>