CI: simplify the logic for rebuilding the containers

right now the check_if_older_than_a_week rule does (in pseudo-code):
- get timestamp of current image or 0
- get timestamp of upstream image or 0
- if upstream image is newer than current image
  copy upstream image into current
- if we are in a scheduled pipeline, or if there is no current image
  (timestamp of 0), rebuild the current image

The ci-templates if-not-exists rule does:
- if there is a current image, exit
- if there is an upstream image, copy it to current and exit
- rebuild

Having the following is equivalent to the current behaviour and
can be used instead of check_if_older_than_a_week:
- if there is an upstream image, copy it to current and exit
- if there is a current image, exit
- rebuild

Because what matters is:

forks should be running the upstream image if available
forks should be running the latest upstream image in the libinput case
forks should be able to rebuild the images if there is no upstream
(change of the image tag)

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>

.gitlab-ci.yml

@@ -117,7 +117,7 @@ variables:
 # is too old or if it is missing some dependencies.
 #
 
-.check_if_older_than_a_week: &check_if_older_than_a_week
+.pull_upstream_or_rebuild: &pull_upstream_or_rebuild
   before_script:
     # log in to the registry
     - podman login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
@@ -125,32 +125,18 @@ variables:
     # get the full container image name (DISTRIB_VERSION still has indirections)
     - IMAGE=$(eval echo "$DISTRIB_FLAVOR/$DISTRIB_VERSION:$TAG")
 
-    # check if our image is already in the current registry and get its date
-    - LOCAL_IMG_DATE=$(skopeo inspect docker://$CI_REGISTRY_IMAGE/$IMAGE | jq -r '.Created' | cut -dT -f1 ||
-                     echo 1970-01-01)
-
-    # get the date of the upstream image
-    - UPSTREAM_IMG_DATE=$(skopeo inspect docker://$CI_REGISTRY/$UPSTREAM_REPO/$IMAGE | jq -r '.Created' | cut -dT -f1 ||
-                        echo 1970-01-01)
-
-    - TODAY_SECS=$(date -u +%s)
-    - LOCAL_IMG_SECS=$(date -u --date="$LOCAL_IMG_DATE" +%s)
-    - UPSTREAM_IMG_SECS=$(date -u --date="$UPSTREAM_IMG_DATE" +%s)
-    - echo "today $TODAY_SECS, local image $LOCAL_IMG_SECS, upstream image $UPSTREAM_IMG_SECS"
-    - echo "image ages $(($TODAY_SECS - $LOCAL_IMG_SECS))s and $(($TODAY_SECS - $UPSTREAM_IMG_SECS))s"
-
-    # if the upstream image is more recent, use it
-    - if [[ $UPSTREAM_IMG_SECS -gt $LOCAL_IMG_SECS ]] ;
+    - |
+      # force rebuild if schedule, reuse otherwise
+      if [[ $CI_PIPELINE_SOURCE != "schedule" ]] ;
       then
-        skopeo copy docker://$CI_REGISTRY/$UPSTREAM_REPO/$IMAGE
-                    docker://$CI_REGISTRY_IMAGE/$IMAGE ;
-        LOCAL_IMG_SECS=UPSTREAM_IMG_SECS ;
+        # pull the latest upstream image if it exists
+        skopeo copy docker://$CI_REGISTRY/$UPSTREAM_REPO/$IMAGE \
+                    docker://$CI_REGISTRY_IMAGE/$IMAGE && exit 0 || true ;
+
+        # check if our image is already in the current registry
+        skopeo inspect docker://$CI_REGISTRY_IMAGE/$IMAGE > /dev/null && exit 0 || true ;
       fi
 
-    # if the image exists and we are not in the scheduled pipeline, exit
-    - test $LOCAL_IMG_SECS -gt 0 -a $CI_PIPELINE_SOURCE != "schedule" && exit 0
-
-
 fedora:28@container-prep:
   extends: .fedora@container-build
   stage: container_prep
@@ -160,7 +146,7 @@ fedora:28@container-prep:
     DISTRIB_FLAVOR: fedora
     DISTRIB_VERSION: $FEDORA_VERSION
     TAG: $FEDORA_TAG
-  <<: *check_if_older_than_a_week
+  <<: *pull_upstream_or_rebuild
 
 fedora:29@container-prep:
   extends: .fedora@container-build
@@ -171,7 +157,7 @@ fedora:29@container-prep:
     DISTRIB_FLAVOR: fedora
     DISTRIB_VERSION: $FEDORA_VERSION
     TAG: $FEDORA_TAG
-  <<: *check_if_older_than_a_week
+  <<: *pull_upstream_or_rebuild
 
 
 ubuntu:18.10@container-prep:
@@ -183,7 +169,7 @@ ubuntu:18.10@container-prep:
     DISTRIB_FLAVOR: ubuntu
     DISTRIB_VERSION: $UBUNTU_VERSION
     TAG: $UBUNTU_TAG
-  <<: *check_if_older_than_a_week
+  <<: *pull_upstream_or_rebuild
 
 ubuntu:18.04@container-prep:
   extends: .ubuntu@container-build
@@ -194,7 +180,7 @@ ubuntu:18.04@container-prep:
     DISTRIB_FLAVOR: ubuntu
     DISTRIB_VERSION: $UBUNTU_VERSION
     TAG: $UBUNTU_TAG
-  <<: *check_if_older_than_a_week
+  <<: *pull_upstream_or_rebuild
 
 
 arch:rolling@container-prep:
@@ -206,12 +192,12 @@ arch:rolling@container-prep:
     DISTRIB_FLAVOR: archlinux
     DISTRIB_VERSION: $ARCH_VERSION
     TAG: $ARCH_TAG
-  <<: *check_if_older_than_a_week
+  <<: *pull_upstream_or_rebuild
 
 .freebsd@container-prep:
   stage: container_prep
   image: $BUILDAH_IMAGE
-  <<: *check_if_older_than_a_week
+  <<: *pull_upstream_or_rebuild
   script:
     - buildcntr=$(buildah from --quiet  myfreeweb/freebsd-cross:latest)
     - buildah run $buildcntr apk add --no-cache $FREEBSD_BUILD_PKGS