Support for listing networks when booting

Example usage in a config.ini:

[cmd:nova.boot_test_infra_mgmt]
@command = nova.boot
networks = net-id=79943449-xece-4bfe-b53a-36b9a1ce4f29

Change-Id: I48d0f4dc244ef3763217df76e1c5e70918e3aebd
Merge "Support for listing networks when booting"