Adjust noobaa tests to handle the external DB type of deployment.

[petr-balogh]

Failures from run:
https://url.corp.redhat.com/9de7ba3

E.g.:
test_noobaa_postgres_cm_post_ocs_upgrade

ocs_ci.ocs.exceptions.CommandFailed: Error during execution of command: oc --kubeconfig /home/jenkins/current-cluster-dir/openshift-cluster-dir/auth/kubeconfig -n openshift-storage get ConfigMap noobaa-postgres-config -n openshift-storage -o yaml.
Error is Error from server (NotFound): configmaps "noobaa-postgres-config" not found

Those two:
test_unidirectional_bucketclass_replication_AWStoGCP_BC_Hybrid_
test_disabled_object_expiration
Fails with:

        source_bucket_name = source_bucket.name
        full_object_path = f"s3://{source_bucket_name}"
        nb_db_pod = Pod(
            **(
>               get_pods_having_label(
                    label=constants.NOOBAA_DB_LABEL_47_AND_ABOVE,
                    namespace=config.ENV_DATA["cluster_namespace"],
                )[0]
            )
        )
E       IndexError: list index out of range

tests/functional/object/mcg/test_bucket_replication.py:410: IndexError

test_verify_noobaa_db_service

                )
E               ocs_ci.ocs.exceptions.CommandFailed: Error during execution of command: oc -n openshift-storage logs noobaa-db-pg-0.
E               Error is Error from server (NotFound): pods "noobaa-db-pg-0" not found

ocs_ci/utility/utils.py:687: CommandFailed