Description of problem:
Create cluster with customized install-config.yaml. But the zones stetting for master did not take effect.

Version-Release number of the following components:
$ ./openshift-install version
./openshift-install v4.0.6-1-dirty

How reproducible:
always

Steps to Reproduce:
1. Create install-config with installer.
# ./openshift-install create install-config --dir test
2. Edit install-config.yaml to change master and worker replicas and instance type as following:
<--snip-->
compute:
- name: worker
  platform:
    aws:
      zones:
      - us-ap-northeast-2a
      - us-ap-northeast-2b
      type: m5.xlarge
  replicas: 3
controlPlane:
  name: master
  platform:
    aws:
      zones:
      - us-ap-northeast-2c
      type: m5.xlarge
  replicas: 3
<--snip-->
platform:
  aws:
    region: ap-northeast-1
<--snip-->
3. Create cluster with above install-config.
# ./openshift-install create cluster --dir test

Actual results:
APIServer launched successfully, the workers created failed.

Expected results:
APIServer should launch failed for the error platform zones.

Additional info:
$ oc get machines qe-piqin2-2ht6z-master-0 -n openshift-machine-api --config=test1/auth/kubeconfig  -oyaml
apiVersion: machine.openshift.io/v1beta1
kind: Machine
metadata:
 <--snip-->
spec:
   <--snip-->
      placement:
        availabilityZone: us-ap-northeast-2c
        region: ap-northeast-1
      publicIp: null
 <--snip-->