Count partitions starting with sd prefix

A test in AttachVolumeShelveTestJSON only counted the partitions
starting with vd making the test fail in the case where
partitions started with sd instead.
This fix also adds sd to the grep regex.

Change-Id: I118a0c3678d5fe0b91aeb24bc80f4d351f71e3cb
Closes-Bug: 1582730
1 file changed