fault: add ability to fault open_by_handel in check_open_handle

From code coverage report, we found that inotify_irmap doesn't test irmap
cache, because we is always able to resolve path from /proc/PID/fd/X.

Current view:	top level - criu - irmap.c (source / functions)			Hit	Total	Coverage
Test:	criu.info		Lines:	40	223	17.9 %
Date:	2016-03-16		Functions:	4	13	30.8 %

This series introduces a new fault to emulate a situation
when a file can't be opened by handle and we have to find
it in the irmap cache/

It's required to test irmap cache. I don't know how to force it
without this patch. Each time when a file can be opened by handle,
its path can be resolved via /proc/PID/fd/X.

Signed-off-by: Andrew Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>