MOD: Add support scaleio backend

[sapd9x]

Hi @j-griffith!
I'm very happy with your code. But It was supported iscsi driver volume type only. I had modified it to work with ScaleIO backend. And It work well. I'm a System Admin not a Developer. So My coding will be bad.
I hope I can contribute to your project.
Thanks

[j-griffith]

Hi greatbn! Thanks for the PR, I have to apoligize that it's been sitting idle for so long. I haven't been keeping up with this project but I'm focusing on it again and will do better.

I'll take a look at the additions you have here, I've been thinking about ways to redesign the connection pieces to make it easier to add connection semantics for things like scale-io and others. I'd like to actually turn this into its own package (or leverage somebody elses). There's also some work the Cinder community has done around a brick plugin that does the same sort of thing, might be interesting to see if there's a way to leverage that as it's pretty comprehensive and has a good deal of maturity.

Let me take a look after Dockercon this week and get back to you on this.

Thank you very much for the PR and welcome!!