[kpartx] Use mapname for device-mapper devices
[kpartx] Use mapname for device-mapper devices

When kpartx is run on a device-mapper device it makes more sense
to use the mapname for generating the device name, not the supplied
commandline arguments. This way we can run kpartx on '/dev/dm-X'
and still get sensible names.

Signed-off-by: Hannes Reinecke <b0d1e9e4a4e27620745ff49be9000da3174a4cc6@suse.de>

vijaychauhan/multipath-tools,unakatsuo/multipath-tools,grzn/multipath-tools-explained,vijaychauhan/multipath-tools,unakatsuo/multipath-tools,unakatsuo/multipath-tools,gebi/multipath-tools,grzn/multipath-tools-explained