Switch make_json_error back to being a function
Switch make_json_error back to being a function

This was originally a function, and then I changed it to a dict because
Flask complained. Now Flask complains that is a dict, so change it back
to being a function.

Change-Id: Iec30b4cf5023be711ac070def00b77e91978d992

openstack/sahara,openstack/sahara