Allow update build cache to run with container image paths of host user

* spack user typically won't be allowed to read the file or its dirname

Change-Id: If54bb738a78e5c70e4b074379b091202c42544c3

.ci/update_build_cache.sh

@@ -35,7 +35,7 @@ source "${SOURCE_DIR}/commons.sh"
 # update script inside the container
 set +e
 # Arugments needed once we switch to singularity3: --writable-tmpfs
-sudo -Eu spack singularity exec\
+sudo -E singularity exec\
     -B "${BUILD_CACHE_OUTSIDE}:${BUILD_CACHE_INSIDE}:rw"\
     "${IMAGE_NAME}" \
-    /opt/spack_install_scripts/update_build_cache_in_container.sh -q || exit 0
+    sudo -Eu spack /opt/spack_install_scripts/update_build_cache_in_container.sh -q || exit 0

.ci/update_build_cache_in_container.sh

@@ -82,6 +82,9 @@ if (( quiet == 1 )); then
     args_progress=""
 fi
 
+# find requires current working directory to be readable by spack user
+cd ${MY_SPACK_FOLDER}
+
 get_hashes_to_store \
     | parallel -r ${args_progress} -j$(nproc) \
         tar Pcfz "${destination_folder}/{}.tar.gz" \"\$\(spack location -i /{}\)\"