Upgrade service VMs using newer version of OVF.
Upgrade is a 2 step process. Update the 'deployment_spec_name' in the
ServiceInstance to the new DeploymentSpec to which the service VMs will be
upgraded, folowed by this 'upgrade' api.
In case of HA, the stand-by service VM will be upgrade first. Once it has been upgraded,
it switches to be the Active one and then the other VM will be upgrade.
POST https://<nsx-mgr>/api/v1/serviceinsertion/services/564dab50-63a0-8b4f-a1f8-20e4d36efc3b/service-instances/564dab50-63a0-8b4f-a1f8-20e4d36efc3c/instance-runtimes?action=upgrade