it doesn't make sense to have a test per STIX version. The
workbench only uses the latest supported STIX version. In
order to make this work, the test suite was modified to
dynamically compute some settings like where to get demo data,
based on the value of stix2.DEFAULT_VERSION.
Switched stix2.DEFAULT_VERSION back to "2.0", since I figure it
should be sync'd up with the 'from .vxx import *' import
statement from the top level package.
