[libmultipath] Update discovery to work with new sysfs layout
[libmultipath] Update discovery to work with new sysfs layout

With the new sysfs layout the parent device of a block device
it 'block', and only the parent of this is the 'real' parent.

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