rectified the disk_name.

Modified add osd script to set weight properly instead of blindly
setting it to 1.0. Now it is calculated based on size of disk
relative to 1TiB.
1TiB disk => weight 1.0
832GiB disk => weight 0.81
Closes-Bug: #1372659

Change-Id: Ib68090115b6770e0110600d3f750ad6cf5a780bc