medium: ui_resource: Only act on resources (#64)

Ensure that the resource sublevel only changes the properties
of actual resources. This allows creating resources that share the same
id as a node uname.

Note that in this case, the node id needs to be different from its
uname.

Fixes #64
medium: ui_resource: Flatten, then filter (#64)

Fix for previous commit: First flatten tags, then filter
out resources.
high: ui_resource: Use correct name for error function (bnc#901453)
high: ui_resource: resource trace failed if operation existed (bnc#901453)
test: Unit test for resource trace