Add regexp for Linux SW RAID devices in /proc/partitions (#678379)

Add regular expression to detect the device entry only (e.g., md127)
and not the partitions (e.g., md127p1).

Linux software RAID devices are listed in /proc/partitions as follows:

# cat /proc/partitions
major minor  #blocks  name
   9   127     523968 md127
 259     0     131072 md127p1
 259     1     262144 md127p2

Part of Bug #678379 - Could not stat device /dev/md/0 - No such file
                      or directory