In places where we have errno value set, such as after calling ptrace(),
it makes sense to use pr_perror as it appends the errno string. This
also fixes missing '\n' at the end (as pr_perror() adds it).

In places where we keep using pr_err(), don't forget to have '\n'.

Cc: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Reviewed-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Acked-by: Andrew Vagin <avagin@odin.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>