fix: ensure the tracked container id is up to date

If the ID file contained an incorrect value, calling :start would say the service is started but :info would still show the container as missing.

Also fix an issue where docker inspect leaked stderr when the container was missing.

Refs dokku/dokku-redis#133

common-functions

@@ -14,7 +14,7 @@ docker_ports_options() {
 get_container_ip() {
   declare desc="Retrieves the ip address of a container"
   declare CONTAINER_ID="$1"
-  docker inspect --format '{{ .NetworkSettings.IPAddress }}' "$CONTAINER_ID"
+  docker inspect --format '{{ .NetworkSettings.IPAddress }}' "$CONTAINER_ID" 2>/dev/null
 }
 
 get_database_name() {