Add ability to configure networks for openstack

Add configuration option `networks`, a list of network UUIDs, to attach to the
source instance.

In some openstack installs, no default network will be attached or the network
with the ability to attach a public floating IP will need to be specified.
Reorder documentation into alphabetical order
Merge pull request #1261 from lflux/openstack-networks-support

Add ability to configure networks for openstack