copy-secrets: rm /opt/bootstrap/assets/manifests/manifests if exists (#…

…49)

Otherwise, it will throw an error when tainting & re-applying null_resource `copy-secrets`
```
mv: cannot move 'manifests' to '/opt/bootstrap/assets/manifests/manifests': Directory not empty
```

aws/container-linux/kubernetes/cl/controller.yaml

@@ -169,6 +169,7 @@ storage:
           sudo mkdir -p /etc/kubernetes/manifests
           sudo mv static-manifests/* /etc/kubernetes/manifests/
           sudo mkdir -p /opt/bootstrap/assets
+          sudo rm -rf /opt/bootstrap/assets/manifests/manifests
           sudo mv manifests /opt/bootstrap/assets/manifests
           sudo mv manifests-networking/* /opt/bootstrap/assets/manifests/
           rm -rf assets auth static-manifests tls manifests-networking