Clean up ML2 Manager

Some things need cleanup in the ML2Manager.

1) Replace sys.exit(1) with raise SystemExit(1)
2) Replace reserved keyword type with network_type

Change-Id: I921bfaec7d3e31503942b3ca4a1b2218c44b14ac
Closes-Bug: #1259646
Merge "Clean up ML2 Manager"