Nested virtualization exposes `/dev/kvm`, which microVMs need. The new
`--enable-nested-virtualization` flag turns it on for the node pool
`setup-gcp` creates. It defaults to on, so pass
`--enable-nested-virtualization=false` for a cluster that does not need
it.
Also, rename the env var `GVISOR_NODE_MACHINE_TYPE` to
`NODE_MACHINE_TYPE` to be consistent with other env vars and to avoid
confusion for microVMs. The old env var still works with a warning.
- [x] Tests pass
- [x] Appropriate changes to documentation are included in the PR
Huy Pham
9f57d78f4f