Change the implementation of action_on_fail

Change the implementation of action_on_fail

Currently when action_on_fail is enabled, the emergency_shell won't be called.
In kdump even though user specify the default action as emergency_shell,
dracut skip it. Now change the implementation of action_on_fail to depend
on a file which is created by kdump when making kdump initrd, then remove it
at the beginning of kdump. This can solve the explicit emergency_shell problem.

And action_on_fail won't need paramenters, remove the relevant description in
dracut man page.

Signed-off-by: Baoquan He <bhe@redhat.com>