Use aptly base image for aptly-api container

`aptly-api` container image is built from aptly image adding command to run
aptly api service.

By using the same image both for aptly and aptly-api we can decrease number
of Drivetrain images and simplify docker image building jobs.

Prod-related: PROD-25633 (PROD:25633)

Change-Id: I16d2efba9da6331eb39cf52c3f725c932610d444
diff --git a/docker/swarm/stack/aptly.yml b/docker/swarm/stack/aptly.yml
index d5b8362..3282641 100644
--- a/docker/swarm/stack/aptly.yml
+++ b/docker/swarm/stack/aptly.yml
@@ -16,7 +16,8 @@
               deploy:
                 restart_policy:
                   condition: any
-              image: ${_param:docker_image_aptly:api}
+              image: ${_param:docker_image_aptly:base}
+              command: 'aptly api serve -no-lock'
               ports:
                 - 18084:8080
               volumes: