fix(builder): pass in http_proxy env variables from host
feat(builder) allow custom slugbuilder and slugrunner images
chore(contrib/coreos): remove unused files

These were once used to generate our default user-data, but haven't
been used in many moons. Leaving them around is both confusing and
crufty.
chore(contrib/coreos): clean up user-data

Our user-data has some unnecessary cruft in it:
* docker.service was out-of-date with the default CoreOS copy (and
actually was never really being applied anyhow).
* docker-tcp.socket is no longer used - docker.socket is defined by CoreOS
* fleet.service was out-of-date, and our change was never being applied (
I think the `start` just took affect)

TESTING: Provisioning should work just as it did before
Merge pull request #1463 from deis/cleanup_contrib_coreos

chore(contrib/coreos): remove unused files
Merge pull request #1464 from deis/cleanup_userdata

chore(contrib/coreos): clean up user-data
fix(contrib/coreos): configure public IP for fleet

We previously defined this, but we did so by overwriting the
stock CoreOS unit file for fleet. That's bad. This enables us
to tweak this setting and still use the stock CoreOS unit file,
which is good.

This is necessary only for Vagrant, but it is safe for cloud
providers as well.

TESTING: provision multi-node, and make sure `fleetctl list-machines`
shows different IPs:
```console
$ fleetctl list-machines
MACHINE		IP		METADATA
4cbcb7c5...	172.17.8.101	-
e00803ec...	172.17.8.100	-
```
Works on EC2 as well...
```
fleetctl list-machines
MACHINE		IP		METADATA
2c985b00...	172.31.12.86	-
43cca2ad...	172.31.35.1	-
ecf3fc08...	172.31.31.144	-
```
fix(controller): add south_migrations to flake8
Merge pull request #1473 from deis/flake8-migrations

fix(controller): add south_migrations to flake8
Merge pull request #1472 from deis/fleet_public_ip

fix(contrib/coreos): configure public IP for fleet
Merge pull request #1462 from soficom/build_custom_image

feat(builder) allow custom slugbuilder and slugrunner images
fix(contrib): remove unnecessary call to echo
fix(contrib): read proper argument
feat(router): Support for WebSockets

Pass upgrade headers through the router to allow applications to
use WebSockets.

Fixes #1061
Merge pull request #1475 from johanneswuerbach/jw-websockets

feat(router): Support for WebSockets
Merge pull request #1450 from wbean1/master

fix(builder): pass in http_proxy env variables from host
docs(*): explicitly specify --hosts parameter for clusters:create

It's convenient to use `local.deisapp.com`, but since we're also
using that as the cluster domain, it's quite confusing.
Merge pull request #1479 from deis/clarify_clusters_create_hosts

docs(*): explicitly specify --hosts parameter for clusters:create
Merge pull request #1474 from deis/fixup-do-script

fix(contrib): digitalocean script arg parsing
docs(contrib/rackspace): Rackspace details

Added Rackspace Load Balancer details.