[server] fix unittest_security for py3k
- use source.binary_to_str instead of str(), helps when the backend
returns memoryviews
- fixup str vs bytes
# re-read ComputedRelation permissions from schema.py now that we're
# able to serialize them
for computedrtype in schema.iter_computed_relations():
sync_schema_props_perms(computedrtype.type)