LP#1152753: make it possible for serial units to be added to copy buckets

LP#1152753: make it possible for serial units to be added to copy buckets

This patch replaces the baseline asset.copy.id fkey constraints with ones
that understand inheritance, and change all existing contstraints to do the
same via upgrade script.

To test
-------
Create some serial units and verify that they can be added to a copy
bucket.

Signed-off-by: Mike Rylander <mrylander@gmail.com>
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>
Signed-off-by: Kathy Lussier <klussier@masslnc.org>