Use list-missing instead of fail in d/rules so builds pass

The workflow for testing Stretch uploads involves using Launchpad
Xenial builders, where the not-installed file is not supported, thus
--fail-missing always fails the build. This is not a useful feature in
a stable release anyway, because rather not introduce any new files.

debian/rules

@@ -180,6 +180,6 @@ get-orig-source:
 	uscan --force-download --verbose
 
 %:
-	dh $@ --parallel --with systemd --fail-missing
+	dh $@ --parallel --with systemd --list-missing
 
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