In certain places, such as after a syscall, we use pr_perror()
to automatically add strerror(errno) to the error message.

In places we're not sure if errno was set by a function we called,
we should use pr_err() instead.

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