phaul: Use Exception class for exceptions, not int

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
iters: Don't work with None FS hauler drivers

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
phaul: Remove old debugging messages

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>