database: PXC does not pick up new database root password

[mook-as]

Describe the bug
When we change the var-pxc-root-password secret and restart the database pod(s), the root database does not get updated; this means:

• The readiness probe will never pass, as it is using the new, modified password instead.
• Any database seeder pods will fail, as they are attempting to use the new root password.

To Reproduce

1. Deploy on minikube with internal database.
2. Apply the following secret rotation config map:

rotate.pxc-root-password.yaml

---
apiVersion: v1
kind: ConfigMap
metadata:
  labels:
    quarks.cloudfoundry.org/secret-rotation: "true"
  name: rotate.pxc-root-password
  namespace: kubecf
data:
    secrets: '[ "var-pxc-root-password" ]'

3. Delete the database-0 pod and let it restart.

Expected behaviour
The database root password is changed.

Actual behaviour
The database root password stays the same; the readiness probe no longer passes.

Environment

• KubeCF ~ d192fa2

Additional context
Found in the context of #703