Make `flocker-deploy` more universal

I'm starting to play with Flocker for the first time. So just thought I'd offer some perspective from fresh eyes. Note that I'm only vaguely aware of other factors that I'm not taking into consideration, eg; #259, #359

Two things struck me about the [current installation docs for the command client](http://doc-dev.clusterhq.com/installation.html);
* The implication that the client can only be installed on Ubuntu. I can't believe this is the case. And is surely off-putting to potential users, when I suspect the client will work perfectly well on Windows even.
* The manipulation of a user's `$PATH`. I consider this bad etiquette and should be avoided at all costs.

So regarding #359. Can Pip's package index not be used for the `flocker-cli` component at least? It has download counts and HTTPS. And then RPMs/debs for the `flocker-node` component? 

I've provided a suggestion `contrib/flocker-deploy-dev.sh` script that overcomes the need for altering `$PATH`. I'm assuming that at some point there will be an official means of installing the client which will place the binary in the system path. Therefore any other means of running the client needs to have another name to avoid conflict and also needs to offer something different, which is why I've made it run the live code from the repo, rather than the setuptools-installed flocker lib version of flocker.

BTW, how do you recommend developing against the command line? Do you use something similar to a `fl-dev` script? Or are you working in a pure TDD style?
This document isn't really intended for developers of Flocker, more for uses of Flocker. And Ubuntu-onlyness of the document will be addressed in next couple of weeks.

As far as developers go: we definitely do TDD. Locally we use `tox` to run tests, so you can rely on "binaries" being installed in `$PATH` (but we have conditional checks so that relevant tests are skipped if binary is not available - see e.g. https://github.com/ClusterHQ/flocker/blob/master/flocker/cli/functional/test_deploy_script.py). Our CI setup using Buildbot makes sure the binaries are also available when tests run, though I haven't bothered to check how exactly. Probably a virtualenv.