implement VM.prototype.setMachineType

[arthuredelstein]

See https://cloud.google.com/compute/docs/reference/v1/instances/setMachineType

[coveralls]

Coverage decreased (-0.07%) to 99.929% when pulling 74d2a74 on arthuredelstein:setMachineType into 9cdcef5 on GoogleCloudPlatform:master.

[arthuredelstein]

Looks like I need to write unit tests. I will work on that (hopefully) later this week.

[stephenplusplus]

Thanks @arthuredelstein!

[stephenplusplus]

@arthuredelstein we just merged a PR that modularized the repo, which will allow us to release modules for each service, instead of having them all in one gcloud package. That brought some significant structure changes, but updating your PR shouldn't be too bad. The file you edited, lib/compute/vm.js, is now packages/compute/src/vm.js. Just move your code into that file, and you'll find the test file you need here: packages/compute/test/vm.js.

[stephenplusplus]

I didn't want to make you do all that, so check it out: #1469. Let me know if it works as you intended!