Add velero self test

Work in progress:

- backup succeeds, and files are stored in the bucket.

- restore complete successfully - but has warning:

    Warnings:
      Velero:     <none>
      Cluster:    <none>
      Namespaces:
        nginx-example:  could not restore, Endpoints "my-nginx" already
        exists. Warning: the in-cluster version is different than the
        backed-up version.

After the restore, the nginx-deployment is missing:

    $ kubectl get all -n nginx-example
    NAME                                    READY   STATUS    RESTARTS   AGE
    pod/nginx-deployment-7c89967545-n2fdb   1/1     Running   0          2m40s
    pod/nginx-deployment-7c89967545-nmznz   1/1     Running   0          2m40s

    NAME               TYPE           CLUSTER-IP      EXTERNAL-IP   PORT(S)        AGE
    service/my-nginx   LoadBalancer   10.103.20.188   <pending>     80:32439/TCP   2m40s

    NAME                                          DESIRED   CURRENT   READY   AGE
    replicaset.apps/nginx-deployment-7c89967545   2         2         2       2m40s

- Need to detect and log the warning after the restore. I could not find
  away to get the restore name programmatically for querying the
  restore.

- Need to cleanup up after the test - delete the deployment and the
  backup.

- Code for using velero is too complicated for a test, I think we need a
  simple `drenv.velero` helper.

Signed-off-by: Nir Soffer <nsoffer@redhat.com>

test/addons/velero/credentials.conf

@@ -0,0 +1,3 @@
+[default]
+aws_access_key_id = minio
+aws_secret_access_key = minio123

test/addons/velero/nginx.yaml

@@ -0,0 +1,48 @@
+# SPDX-FileCopyrightText: 2017 the Velero contributors
+# SPDX-License-Identifier: Apache-2.0
+
+---
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: nginx-example
+  labels:
+    app: nginx
+
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: nginx-deployment
+  namespace: nginx-example
+spec:
+  replicas: 2
+  selector:
+    matchLabels:
+      app: nginx
+  template:
+    metadata:
+      labels:
+        app: nginx
+    spec:
+      containers:
+      - image: nginx:1.17.6
+        name: nginx
+        ports:
+        - containerPort: 80
+
+---
+apiVersion: v1
+kind: Service
+metadata:
+  labels:
+    app: nginx
+  name: my-nginx
+  namespace: nginx-example
+spec:
+  ports:
+  - port: 80
+    targetPort: 80
+  selector:
+    app: nginx
+  type: LoadBalancer