Support GCE API v1

So this is a bit of a stretch goal for 1.7.0, but GCE has gone GA and moved to API v1, which...well, https://developers.google.com/compute/docs/transition-v1 - it's got a number of breaking changes from v1beta16 and earlier. Most notably, instance creation and images are now more than a little different. The images from v1beta16 and earlier with Google-provided kernels don't work with v1, the kernel resource is just gone completely, and most annoyingly, you no longer can create instances from images directly. Instead, you have to first create a root persistent disk from an image, and then specify that disk when creating the instance. When you get an instance's information, it no longer has anything about the image it was created from - instead you've got to go through the disk to see what its source image is, but even that's a bit odd, since the current API reference doesn't actually include the sourceImage in the list of fields for disk resources, though it's pretty strongly implied that it should be there...bah.

Anyway, I'm going to try to get this done for 1.7.0, but given the timeframe, it may not be completed in time. v1beta16 is supposed to stick around until March, so we've got some cushion to get out 1.7.1 with v1 support if needed.