completion: filter templates from restartable units

Since c6a373a263, we might encounter unit templates via the
'list-units' verb. These aren't restartable (and we throw errors), so
make sure they're filtered out of the completion options.

fixes downstream bug: https://bugs.archlinux.org/task/41719

shell-completion/bash/systemctl.in

@@ -182,7 +182,7 @@ _systemctl () {
                 comps=$( __filter_units_by_property $mode CanStart yes \
                       $( __get_all_units $mode \
                         | while read -r line; do \
-                                [[ "$line" =~ \.(device|snapshot|socket|timer)$ ]] || echo " $line"; \
+                                [[ "$line" =~ @\.|\.(device|snapshot|socket|timer)$ ]] || echo " $line"; \
                         done ))
                 compopt -o filenames