generic/084: use src/multi_open_unlink to replace tail command

generic/084: use src/multi_open_unlink to replace tail command

generic/084 try to run 'tail' command, tail will use inotify.
There're some limit about the number of inotify. For example
fs.inotify.max_user_instances specifies an upper limit on
the number of inotify instances that can be created per real
user ID.

When I test on a machine with 154 cpu cores, this case run
failed, and hit many warning likes:

    +tail: inotify cannot be used, reverting to polling: Too many open files

Because the fs.inotify.max_user_instances is 128, so if we
try to tail 154 files, it will be failed.

So use src/multi_open_unlink to instead of tail will avoid
this problem.

Signed-off-by: Zorro Lang <zlang@redhat.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>