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?
That's not quite the core point I'm making. The symbolic link is just an idea for *developers* hacking on Flocker, not end users. Therefore the symbolic link would never be created automatically by an install script, it would have to be manually entered into the command line. This of course circles back to my curiosity about your recommended method for developing the CLI component. Do you develop by writing tests first and using test output to guide you, ie TDD? Or do you have some means of hooking into setuptool's `pkg_resources.load_entry_point` so you can run the command line 'binary' against the live code base?

Of course the way most people will encounter the `flocker-deploy` command through the .deb/.rpm and so will never have to be concerned with these nuances.

To be honest, the main thing I'd like to see changed is the implication that `flocker-deploy` only works on Ubuntu.