introduce initial, unit tested google cloud platform element set

This is the minimum needed for my codelab (compute engine is the first and only cloud product supported, and only part of GCE at that) but I think it also builds a decent starting point for cloud polymer components. I defined a naming convention for elements and files to hopefully avoid a proliferation of confusing and inconsistent names used across the many cloud products.
I like the current attribs for the boot disk because it provides easier usability but I'd also like to add a disk object for power users. Beyond that, one can start a VM with auxiliary disks beyond the boot drive, and there's no way to express that with my current attribute set. Having the disk attributes be a "disks" (plural) attrib, which takes an array of json objects would be very powerful. I'll add an issue to do that but don't want to try to sweep that in now as I'm crunching this for next week's codelab.