testplan: Add Starlark functions to create VMTestPlan protos.

- Follows similar patterns to Starlark fns. to create HWTestPlan
protos.

- Backwards compatibility with CTPV1 will be supported in next CL,
in this CL testplan returns an error when VMTestPlan protos are
created.

BUG=b:218319842
TEST=CQ

Change-Id: Ic80657219697fc6cc29f939a8b6a7bd9925ca5fd
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/3726853
Tested-by: Andrew Lamb <andrewlamb@chromium.org>
Commit-Queue: Andrew Lamb <andrewlamb@chromium.org>
Reviewed-by: Navil Perez <navil@google.com>
7 files changed