T3663: add  pre_hook argument to util.wait_for_inotify
T3663: add  pre_hook argument to util.wait_for_inotify

When waiting for processes that don't take long,
we need add an inotify watcher _before_ starting that process.

The pre-hook arguments allows the user to pass a () -> () anonymous function
to be called before adding a watch.

vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x