We want to be compatible with whatever docker the user has; `weave
run` is the only command that passes on arbitrary args to docker
(i.e., that doesn't have a fixed set of docker features that it
needs).
To make this workable we still need to do some things on the remote
host: the IP attachment and figuring out the DNS settings (since those
may depend on the bridge IP).
This is to make a visible break with previous releases, such that a
newly downloaded weave script will definitely work.
Without this change in name, an existing weavetools image that doesn't
include the script might be invoked, resulting in a confusing message
for the user.