Require the --agent-directory (by default "/run/systemd/ask-password") to be an actual directory; fail otherwise.
* dracut-module/password-agent.c (main): Make ENOTDIR from add_inotify_dir_watch() result in EX_OSFILE. (add_inotify_dir_watch): Add "IN_ONLYDIR" flag to inotify_add_watch(). (test_add_inotify_dir_watch_nondir): New test. (run_tests): Add new test.