fault-inject: add ratelimit option

Current debug levels are not optimal.  Especially if one want to provoke
big numbers of faults(broken device simulator) then any verbose level will
produce giant numbers of identical logging messages.  Let's add ratelimit
parameter for that purpose.

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Acked-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>