Support --help as well as -h

The majority of scripts in this directory (17 vs 14) support both -h and
--help. Switch this script to be part of the majority.

Help text is modified to clarify the fact that --bm-networks is
optional, but if not supplied the script is a no-op

Change-Id: I1c57f522ea3b26969538674d0cbc6c7be4bba365