various: do not include file names directly in error messages

git grep -l 'Failed to open /'|xargs sed -r -i 's|"Failed to open (/[^ ]+): %m"|"Failed to open %s: %m", "\1"|g'
git grep -l $'Failed to open \'/'|xargs sed -r -i $'s|"Failed to open \'(/[^ ]+)\': %m"|"Failed to open %s: %m", "\\1"|g'
git grep -l "Failed to open /"|xargs sed -r -i $'s|"Failed to open (/[^ ]+), ignoring: %m"|"Failed to open %s, ignoring: %m", "\\1"|g'
+ some manual fixups.

src/machine/machined.c

@@ -179,7 +179,7 @@ static int manager_enumerate_machines(Manager *m) {
                 if (errno == ENOENT)
                         return 0;
 
-                return log_error_errno(errno, "Failed to open /run/systemd/machines: %m");
+                return log_error_errno(errno, "Failed to open %s: %m", "/run/systemd/machines");
         }
 
         FOREACH_DIRENT(de, d, return -errno) {