Tag the docker images as "latest"

We will use this tag in qtbase to refer to the image to run, because
with the current sha1tree() tag, every minor change in the docker images
requires synchronized changes between repositories.

Task-number: QTBUG-79867
Change-Id: If94eb6dd8b97526b589e58064837bc6554fed79c
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

coin/provisioning/common/shared/testserver/docker_images.sh

@@ -51,18 +51,20 @@ sha1tree () {
         sort | ${SHASUM-sha1sum} | cut -d ' ' -f 1
 }
 
-# Using SHA-1 of each server context as the tag of docker images. A tag labels a
-# specific image version. It is used by docker compose file (docker-compose.yml)
-# to launch the corresponding docker containers. If one of the server contexts
-# (./apache2, ./danted, ...) gets changes, all the related compose files in
-# qtbase should be updated as well.
+# A tag labels a specific image version. In the docker compose file
+# (docker-compose.yml) that launches the containers, the tag used is
+# "latest". Here the images are also tagged with the SHA1 of each server
+# context, so if needed we can modify docker-compose.yml to launch a very
+# specific image, thus providing a way to stage backwards-incompatible changes
+# across repositories.
 
 source "$SERVER_PATH/settings.sh"
 
 for server in $testserver
 do
     context="$SERVER_PATH/$server"
-    docker build -t qt-test-server-$server:$(sha1tree $context) $context
+    tag=$(sha1tree $context)
+    docker build -t qt-test-server-$server:$tag -t qt-test-server-$server:latest  $context
 done
 
 docker images