Generate static delta after OSTree commit

After generating the commit, we can use the tip of the branch
to generate the static delta that exactly matches the commit.
Use image_name as the name of the static delta to help distinguish
between each other when in a repository.
The name also contains the pipeline version in the name, hence it
is possible to sort by filename to get the most recent static delta.

Signed-off-by: Frédéric Dalleau <frederic.dalleau@collabora.com>

Jenkinsfile

@@ -259,6 +259,15 @@ def buildOStree(architecture, type, board, debosarguments = "", repo = "repo") {
         -t message:${release}-${type}-${architecture}-${board}_${PIPELINE_VERSION} \
         -t ostree:${repo} \
         ${WORKSPACE}/${osname}-ostree-commit.yaml""")
+
+  sh(script: """
+      cd ${PIPELINE_VERSION}/${architecture}/${type}
+      ostree --repo=${repo} static-delta generate \
+        --empty \
+        --to=${branch} \
+        --inline \
+        --min-fallback-size=1024 \
+        --filename ${image_name}.delta""")
 }
 
 /** Generate the image name