Description of problem:
The default mhc machine-api-termination-handler couldn't watch spot instance, if we create some spot instances, the mhc total torgets is 0.

Version-Release number of selected component (if applicable):
$ oc get clusterversion
NAME      VERSION                             AVAILABLE   PROGRESSING   SINCE   STATUS
version   4.7.0-0.nightly-2020-12-09-112139   True        False         3d1h    Cluster version is 4.7.0-0.nightly-2020-12-09-112139

How reproducible:
always

Steps to Reproduce:
1. Create a spot instance with "preemptible: true"
2. Check mhc machine-api-termination-handler
3.

Actual results:
The default mhc machine-api-termination-handler total targets is 0.

$ oc get ds
NAME                              DESIRED   CURRENT   READY   UP-TO-DATE   AVAILABLE   NODE SELECTOR                                  AGE
machine-api-termination-handler   1         1         1       1            1           machine.openshift.io/interruptible-instance=   3d3h

$ oc get machine
NAME                              PHASE     TYPE            REGION        ZONE            AGE
zhsungcp11-bjhl5-master-0         Running   n1-standard-4   us-central1   us-central1-a   3d3h
zhsungcp11-bjhl5-master-1         Running   n1-standard-4   us-central1   us-central1-b   3d3h
zhsungcp11-bjhl5-master-2         Running   n1-standard-4   us-central1   us-central1-c   3d3h
zhsungcp11-bjhl5-worker-a-5k5cd   Running   n1-standard-4   us-central1   us-central1-a   3d3h
zhsungcp11-bjhl5-worker-b-vwv2r   Running   n1-standard-4   us-central1   us-central1-b   3d3h
zhsungcp11-bjhl5-worker-c-54m7p   Running   n1-standard-4   us-central1   us-central1-c   163m


$ oc get mhc
NAME                              MAXUNHEALTHY   EXPECTEDMACHINES   CURRENTHEALTHY
machine-api-termination-handler   100%           0                  0

$ oc logs -f machine-api-controllers-6dddcb4fff-fjsxv -c machine-healthcheck-controller
I1211 14:11:05.851755       1 machinehealthcheck_controller.go:153] Reconciling openshift-machine-api/machine-api-termination-handler
I1211 14:11:05.851803       1 machinehealthcheck_controller.go:171] Reconciling openshift-machine-api/machine-api-termination-handler: finding targets
I1211 14:11:05.851880       1 machinehealthcheck_controller.go:228] Remediations are allowed for openshift-machine-api/machine-api-termination-handler: total targets: 0,  max unhealthy: 100%, unhealthy targets: 0
I1211 14:11:05.859989       1 machinehealthcheck_controller.go:263] Reconciling openshift-machine-api/machine-api-termination-handler: no more targets meet unhealthy criteria

$ oc edit machine zhsungcp11-bjhl5-worker-c-54m7p
apiVersion: machine.openshift.io/v1beta1
kind: Machine
metadata:
  annotations:
    machine.openshift.io/instance-state: RUNNING
  creationTimestamp: "2020-12-14T02:56:43Z"
  finalizers:
  - machine.machine.openshift.io
  generateName: zhsungcp11-bjhl5-worker-c-
  generation: 2
  labels:
    machine.openshift.io/cluster-api-cluster: zhsungcp11-bjhl5
    machine.openshift.io/cluster-api-machine-role: worker
    machine.openshift.io/cluster-api-machine-type: worker
    machine.openshift.io/cluster-api-machineset: zhsungcp11-bjhl5-worker-c
    machine.openshift.io/instance-type: n1-standard-4
    machine.openshift.io/region: us-central1
    machine.openshift.io/zone: us-central1-c
  name: zhsungcp11-bjhl5-worker-c-54m7p
...
spec:
  metadata:
    labels:
      machine.openshift.io/interruptible-instance: ""
  providerID: gce://openshift-qe/us-central1-c/zhsungcp11-bjhl5-worker-c-54m7p
  
    
Expected results:
The total target number is equal to the spot instance number.

Additional info: