Switch example back to kvm2

The podman driver causes too many trouble and the only environment that
needs it is the test env used in the drenv tests. Using kvm2 makes it
easy to debug and test change to drenv itself.

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

test/envs/example.yaml

@@ -6,8 +6,8 @@
 name: example
 templates:
   - name: "example-cluster"
-    driver: podman
-    container_runtime: cri-o
+    driver: kvm2
+    container_runtime: containerd
     workers:
       - addons:
           - name: example