The no_proxy list should only contain domains, hostnames, IP addresses
and networks, but docker_registry is often in the form ip_address:port.

Use urlsplit to extract the hostname from the docker_registry variable
after prepending http:// to turn it into a valid URL.

Also add missing infra-vms to hosts in proxy.yml.

Change-Id: I6424fc405894514a63fb2b641637bbb9d5c070c0