Rework sysfs device handling in multipathd

Rework sysfs device handling in multipathd

Relying on sysfs devices has the disadvantage that the device
might already been gone by the time we look at it. And we don't
actually need it for eg device-mapper events as we can get all
required information via the device-mapper ioctl.
So only access sysfs if we absolutely have to and try to get
the information from other places if possible.

Signed-off-by: Hannes Reinecke <hare@suse.de>