The workaround of using deepcopy calls on the PortBinding
and PortBindingLevel objects prevents the port relationship
from being loaded to bump its revision because it then fails
to merge.
So in order to allow port bindings to bump the revision we
need to stop using sqlalchemy objects in the PortContext. This
patch adds a new snapshot object that just copies the column
values and provides a method to reconcile them back into the
session.
This workaround can go away after we switch to using OVOs, but
this needs to be backportable so we can't just wait for OVO
adoption.
Partial-Bug: #1699034
Change-Id: Ib85ec8182117fa3c4844dabfffe881e38e68b556
0f536d5a25