Fix ClusterRoleBinding namespace setting on kubectl-minio

[cesnietor]

Fixes issue #479 for clusterRoleBinding not being set correctly for defined namespaces.

Since rbacv1.ClusterRoleBinding.Subjects is not a pointer, we have to
replace the array instead of modifying the values.

To test:

1. Build operator locally like :

 make build TAG="minio/operator:test" &&  kind load docker-image minio/operator:test

2. Build plugin locally like

cd kubectl-minio && go build

3.and run :

 kubectl create ns minio-operator && ./kubectl-minio init -n minio-operator --image=minio/operator:test --output=false

This should create operator, console and you should be able to access operator with no 403 (forbidden) issues.