Now we have some use cases about set/unset properties,
try to redefine devref to find out a best and easiest
solution to keep commands simple and clearly.
Five use cases exist in property action, "append",
"update", "remove", "clean", "override", the following
rules can cover all these use cases:
1. append ==> "set --property new-key=value"
2. update ==> "set --property existed-key=new-value"
3. remove ==> "unset --property existed-key"
4. clean ==> "set --no-property"
5. clean ==> "unset --all-property"
6. override ==> "set --no-property --property new-key=value"
Related blueprint support-no-property-in-aggregate and
blueprint allow-overwrite-set-options.
Change-Id: If86daf6989d8e0ad0dc6e590d7636be7d5203a18
29f78500db