title: POSTGRES_USER not taken into account
body: <p>I'm trying to deploy postgres as a <code>StatefulSet</code> on <code>k3d</code>.</p>
  <p>I set the environment variable <code>POSTGRES_USER</code>, but when I try to connect to the db, it isn't taken into account and I see that authentication has failed. I can login with the password <code>pgpassword</code> and default user <code>postgres</code>.</p>
  <p>Why isn't the <code>POSTGRES_USER</code> taken into account?</p>
  <p>This is my yml:</p>
  <pre class="lang-yaml prettyprint-override"><code>apiVersion: apps/v1
  kind: StatefulSet
  metadata:
    name: postgresql-db
  spec:
    serviceName: postgresql-db-service
    selector:
      matchLabels:
        app: postgresql-db
    replicas: 2
    template:
      metadata:
        labels:
          app: postgresql-db
      spec:
        containers:
          - name: postgresql-db
            image: postgres:latest
            volumeMounts:
              - name: postgresql-db-disk
                mountPath: /data
            env:
              - name: POSTGRES_USER
                value: pguser
              - name: POSTGRES_PASSWORD
                value: pgpassword
              - name: PGDATA
                value: /data/pgdata
        volumes:
          - name: postgresql-db-disk
            hostPath:
              # directory location on host
              path: /opt/x/projects/tilt_test/data/
              # this field is optional
              type: DirectoryOrCreate
  </code></pre>