Make weaveDNS use the docker bridge IP instead of its own

This means the `--dns` setting for containers will work even if the
weavedns container is restarted (and assigned a new docker network
IP).
Catch the README up with the change in IP used
building weave requires a recent docker
We know for sure it builds with 1.3.0 and not 1.0.1. I can't be
bothered to check every version inbetween, so let's just say we
require 1.3.0.

Closes #220.
Merge pull request #211 from squaremo/issue201_use_docker_bridge_ip

LGTM.  Closes #201
Revert "Use Docker bridge IP for DNS"
Merge pull request #232 from zettio/revert-211-issue201_use_docker_bridge_ip

Revert "Use Docker bridge IP for DNS"
Add --with-dns option to weave run
Two minus signs
Improve kernel version matcher (close #185)
Merge PR #231: Improve kernel version matcher

Fixes issue #185
Simplify arg parsing on weave run
Undid extra check that there is at least one argument to 'docker run'
Merge branch '208_opt_in' of github.com:bboreham/weave into pr234_with_dns
Populate DNS when starting the weaveDNS container
Only get the DNS container IP once

`populate_dns` previously used http_call, which looks up the IP for a
container each time. I've factored the HTTP bit after the IP look-up
in http_call out, so it can be used directly. This involved switching
arguments around to make the tail call easier.
Wait for weaveDNS HTTP to be running before sending it names

This adds a no-op endpoint to the HTTP API at `/status`. The script
simply tries this until it succeeds or gets bored.