Made changes to osd setup code to support loop device

Loopback device will be used to automatically generate disks for testing.

Loop devices have different naming scheme for the partitions
Partition 1 on /dev/sda is /dev/sda1 and 2 is /dev/sda2, but in case of
loop device, partition1 of /dev/loop0 is /dev/loop0p1 and 2 is /dev/loop0p2.
So changes are required to set proper partition names.
This is because of the difference in partition naming - device name of first partition of normal disk device is /dev/sda1 where same for loop device is /dev/loop0p1. 

So we need to add "p" as partition prefix to get correct partition name.