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>
Depends-on: Ib32637da86e72ff22a7c5684a3f179b91f09406f
Change-Id: Icc5407c722e2cb7d1d38fa695f6e4b4f40f2e67b
a56b62bbee