pr_perror(): don't end message with a period

When pr_perror is used, an error message is appended with a comma
and an strerror(errno), so we should not put a period at the end,
otherwise we'll end up with something like this:

	Error: Can't bind.: Permission denied

Found by git grep -w pr_perror | grep '\."'

Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>