Log function pr_perror() automatically adds
 - numeric errno value
 - string errno value (aka strerror(errno), aka %m)
 - a newline

So, its callers don't have to do all these things.

While at it, also
 - fix or improve some message texts
 - replace fnprintf() with pr_perror()
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Acked-by: Andrew Vagin <avagin@gmail.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>