Adds plan-remove-role command to CLI

Adds plan-remove-role command to command line interface.
Adds test for plan-remove-role command.
Modifies PlanManager's remove_role method to use json_request directly
and return Plan.
Modifies tests for this change.

Change-Id: I7b2771ca4f1194c8c15eeebb45febd099e60351c
Merge "Adds plan-remove-role command to CLI"