I think if you learn Rails, build an app in it, and open-source it on GitHub or similar, that would be fairly strong evidence that you know what you're doing.
If I were in your position, I would go to the source ( http://www.uscis.gov/ ) and examine the visa categories that are available to you. Immigration law is complicated, but not as complicated as, say, the tax code. If you've completed a Masters in CS, you can probably navigate it yourself. Protip: Do not lie or mislead USCIS or USCBP (i.e. customs) as you can be banned from the country easily.
Unfortunately it may be very difficult for you to get a visa to DevBootcamp as it's almost certainly not a SEVP-certified school, so ICE / USCIS won't grant visas to people to attend, and you can't just get a tourist visa if you're intending to study. I would instead learn Rails yourself, start / open source a project, and try to get a job offer here with a company that will help with your visa situation (once you have a job offer, immigration becomes much easier as long as the company is game). I guess my main question becomes, is DevBootcamp the only reason you want to move to the US?
I'm an immigrant from Canada but I'm more familiar with family-based immigration as that's how I came across (fiance visa).