Values:
PROVISIONING_MODEL_UNSPECIFIED (0):
Unspecified.
STANDARD (1):
Standard VM.
SPOT (2):
SPOT VM.
PREEMPTIBLE (3):
Preemptible VM (PVM).
Above SPOT VM is the preferable model for
preemptible VM instances: the old preemptible VM
model (indicated by this field) is the older
model, and has been migrated to use the SPOT
model as the underlying technology. This old
model will still be supported.