tree-wide: fix incorrect uses of %m

In those cases errno was not set, so we would be logging some unrelated error
or "Success".

src/test/test-loopback.c

@@ -31,7 +31,7 @@ int main(int argc, char* argv[]) {
 
         r = loopback_setup();
         if (r < 0)
-                log_error("loopback: %m");
+                log_error_errno(r, "loopback: %m");
 
         return r >= 0 ? EXIT_SUCCESS : EXIT_FAILURE;
 }