Add packages to buildcache

.gitlab-ci.yml

@@ -107,6 +107,10 @@ spack:install:
       --only-concrete
       --fail-fast
       --show-log-on-error
+    - spack/bin/spack -e stacks/${stack} buildcache create
+      --update-index
+      --key EDC904DCE3D2E84E
+      /buildcache
   after_script:
     - if [ ! -e spack-install.xml ]; then
         echo "{}" > spack-install.xml