check_networks task result is non-consistent

Result field of check_networks message have several parameters which must have 'dict' type to be interpretted correctly on UI side. So, UI cannot recognize messages correctly for a number of cases.

Sample message:
{"status": "error", "name": "check_networks", "cluster": 1, "result": [{"errors": ["cidr"], "id": [4, 5], "range_errors": ["192.0.0.0/2", "192.168.1.0/24"]}], "progress": 100, "message": "Address space intersection between networks:\nmanagement, storage.", "id": 5, "uuid": "12c20fd2-5561-44da-b4a8-2880d41897fa"}

"errors" and "id" fields must always have 'dict' type. "range_errors" fields is to be removed as it is not being used anywhere.