init-storage: Create intermediate dirs in /etc

When creating writable paths in the `/etc` subvolume, the `setup_etc`
function needs to create intermediate directories before copying
existing files from the root filesystem.  Without this step, `cp` will
fail with a "no such file or directory" error, referring to the
destination path.

overlay/usr/libexec/init-storage

@@ -136,6 +136,11 @@ setup_etc() {
         while read type path; do
             if [ ! -e "${tmpdir}/${path}" ]; then
                 if [ -e /etc/"${path}" ]; then
+                    case "${path}" in
+                    */*)
+                        mkdir -p "${tmpdir}/${path%/*}"
+                        ;;
+                    esac
                     cp -ca /etc/"${path}" "${tmpdir}/${path}"
                 elif [ "${type}" = d ]; then
                     mkdir -p "${tmpdir}/${path}"