Add possibility to create volumes implicitly.

dvbackup.sh

@@ -67,9 +67,13 @@ restore_all() {
         volume_name="${tarball%.tar}"
         echo "$volume_name -> $volume"
         if ! "$DOCKER" volume inspect "$volume_name" 1>&2 2>/dev/null; then
+            if echo "$DVB_CREATE_VOLUME" | grep -Eiq 't|true|1|y|yes'; then
+                "$DOCKER" volume create "$volume_name"
+            else
                 echo "Error: no such volume $volume_name" >&2
                 exit 4
             fi
+        fi
         restore "$tarball" "$volume_name"
     done
 }