Dump Windows version information during cluster bringup.
Introduce Get-InstanceMetadata which can be used to fetch non-"attribute" metadata values.
Also switches to the most recent 64-bit version of OpenSSH for Windows. Tested: PROJECT=${CLOUDSDK_CORE_PROJECT} KUBERNETES_SKIP_CONFIRM=y NUM_NODES=2 \ NUM_WINDOWS_NODES=2 KUBE_GCE_ENABLE_IP_ALIASES=true TEST_CLUSTER=true \ ./cluster/kube-up.sh