* Re-add the destination container to the controller spec
This fix is necessary to avoid data plane downtime during an upgrade to
stable-2.6. All existing older proxies will continue to send requests to
this destination container, until the data plane is restarted.
On restart, the new pods will start forwarding their requests to the new
linkerd-dst service.
* Use the 2.6 destination service fqdn
* Fixed unit tests
* Fix integration test failure
Signed-off-by: Ivan Sim <ivan@buoyant.io>