Fix bluestore disk naming format in kolla-ansible

The current bluestore disk label naming is inconsistent with the
filestore. The filestore naming format is that the disk prefixes
belonging to the same osd are the same and the suffixes are
different.

This patch keeps the bluestore's disk naming as well.

Change-Id: I71dda29fc4a6765300ce7bb173d2c448c24f6eca