Machine should manage credentials for drivers

[dave-tucker]

I find that managing env variables for the various drivers to be a little clumsy. Not only are there issues related to me accidentally putting these in my .zshrc which is hosted on GitHub, but it's tricky to manage multiple accounts with the same provider.

For example, consider DigitalOcean, where I have a "personal" account and a "company" account.
To perform operations on one, or the other, I'd need to make sure to source the correct file first or the API calls would fail.

I'd like to see something along the lines of:

docker-machine account create -d digitalocean dave
... prompts for the required credentials...
Account "dave" for DigitalOcean created successfully

docker-machine account create -d digitalocean work
... prompts for the required credentials...
Account "work" for DigitalOcean created successfully 

docker-machine create -d digitalocean --account dave

I would expect machine to securely store the minimum amount of information required. Perhaps in ~/.docker/accounts

[ehazlett]

We are looking at adding support for this in #773. Not sure on timeline though.

[dave-tucker]

Cool! Thanks @ehazlett

[ehazlett]

yw! this is ref'd in that issue -- feel free to re-open if you have other ideas or questions. thanks!