Allow disabling the ovn provider in scen013

Same reason as in https://review.opendev.org/#/c/713960/. The lack of
packaging of master OVN provider driver prevents the Octavia API from
starting as it tries to load the OVN driver but the code is not present.

Change-Id: I680cf82b6e241da9d569c90b44814b1023bb5b69

ci/environments/scenario013-standalone.yaml

@@ -31,6 +31,9 @@ parameter_defaults:
   OctaviaCaKeyPassphrase: 'upstreamci'
   OctaviaManageNovaFlavor: true
   OctaviaGenerateCerts: true
+  # TODO(cgoncalves): re-enable once RDO package ovn-octavia-provider is available (https://review.rdoproject.org/r/#/c/25972/)
+  #                   and installed in Kolla container
+  OctaviaEnableDriverAgent: false
   Debug: true
   GlanceBackend: 'file'
   ContainerCli: podman