Add admin utilities to list and clean backend logical switches that does
not exist in neutron.
Usage:
nsxadmin -r orphaned-networks -o list
nsxadmin -r orphaned-networks -o nsx-clean --property nsx-id=<id>
(Cherry picked from: Icc5407c722e2cb7d1d38fa695f6e4b4f40f2e67b)
Change-Id: Ia90669f80ddd55ad57acb6f899c149db63705a5b