Fixes #7041: fixed incorrect belongs_to mappings

:conditions reference columns from the local (to the relation) table,
while the condition is applied to the remote side of the association.
The condition can be removed, as it's redundant anyway.
refs #6161 - Add test to make sure override is marked on create
fixes #7336 - editing compute resource should not clear existing attributes from the form
fixes #3544 - Editing an oVirt compute resource allows changing the type, which is unsupported