Description of problem:
Create a machine set availabilityZone to a not exist zone, logs show subnet not exist 

Version-Release number of selected component (if applicable):
$ oc get clusterversion
NAME      VERSION                           AVAILABLE   PROGRESSING   SINCE     STATUS
version   4.0.0-0.alpha-2019-01-09-005354   True        False         3h        Cluster version is 4.0.0-0.alpha-2019-01-09-005354

How reproducible:
Always


Steps to Reproduce:
1. Create a machine set availabilityZone to a non-existent zone
apiVersion: cluster.k8s.io/v1alpha1
kind: Machine
metadata:
  finalizers:
  - machine.cluster.k8s.io
  labels:
    sigs.k8s.io/cluster-api-cluster: zhsun
    sigs.k8s.io/cluster-api-machine-role: worker
    sigs.k8s.io/cluster-api-machine-type: worker
  name: zhsun-worker-us-east-2a-zone-not
  namespace: openshift-cluster-api
spec:
  metadata:
    creationTimestamp: null
  providerConfig:
    value:
      ami:
        arn: null
        filters: null
        id: ami-064936a7bd92922ca
      apiVersion: awsproviderconfig.k8s.io/v1alpha1
      credentialsSecret: null
      deviceIndex: 0
      iamInstanceProfile:
        arn: null
        filters: null
        id: zhsun-worker-profile
      instanceType: m4.large
      keyName: null
      kind: AWSMachineProviderConfig
      loadBalancers: null
      metadata:
        creationTimestamp: null
      placement:
        availabilityZone: us-east-2alllll
        region: us-east-2
      publicIp: null
      securityGroups:
      - arn: null
        filters:
        - name: tag:Name
          values:
          - zhsun_worker_sg
        id: null
      subnet:
        arn: null
        filters:
        - name: tag:Name
          values:
          - zhsun-worker-us-east-2a
        id: null
      tags:
      - name: openshiftClusterID
        value: 5cbc3a6b-5641-4638-b8ee-2bdc52d84d73
      - name: kubernetes.io/cluster/zhsun
        value: owned
      userDataSecret:
        name: worker-user-data
  providerSpec: {}
  versions:
    kubelet: ""
2. Check machine-controller logs
$ oc logs -f clusterapi-manager-controllers-7d56dd5857-zvc6r -c machine-controller
I0107 09:29:40.317055       1 actuator.go:109] creating machine
I0107 09:29:40.317065       1 utils.go:151] Falling to providerConfig
I0107 09:29:40.335110       1 instances.go:44] no stopped instances found for machine zhsun-worker-us-east-2a-zone-not
I0107 09:29:40.347964       1 instances.go:131] Using AMI ami-064936a7bd92922ca
I0107 09:29:40.347982       1 instances.go:73] Describing security groups based on filters
I0107 09:29:40.382091       1 instances.go:108] Describing subnets based on filters
E0107 09:29:40.436996       1 actuator.go:103] Machine error: error launching instance: error getting subnet IDs: no subnet IDs were found,
E0107 09:29:40.437011       1 actuator.go:112] error creating machine: error launching instance: error getting subnet IDs: no subnet IDs were found,
I0107 09:29:40.437020       1 actuator.go:161] updating machine conditions
I0107 09:29:40.437245       1 actuator.go:152] status unchanged


Actual results:
Logs show no subnet IDs were found.

Expected results:
Logs show no availabilityZone found.

Additional info: