criu/*: annual pr_perror() usage sanitization

When using pr_perror(), we should not end the message with \n,
as it is added automatically.

Unfortunately, I still can't figure a way to check this at compile
time, so here's the annual patch.

travis-ci: success for Assorted nitpicks
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>