add_node_capability and rm_node_capability unable to save changes to db

Changes to elements in existing node.properties dictionary will not get
saved to database by node.save(context) method. The properties dictionary
needs to be replaced by a new one to get the changes to be saved in the db.

Change-Id: I3bb65d00e141aedcb1278c1a700d12c9b29f7232
Closes-bug:#1371816
Merge "add_node_capability and rm_node_capability unable to save changes to db"