osd: Change PG Deletion cost for mClock

osd: Change PG Deletion cost for mClock

With the osd_delete_sleep_ssd and osd_delete_sleep_hdd options disabled with mClock, it was noticed that PG deletion was completing much faster with mClock scheduler.
In order to give mClock a more accurate cost of the PG Deletion operation, we calculate it by taking into consideration how many objects are being deleted.

Signed-off-by: Aishwarya Mathuria <amathuri@redhat.com>
(cherry picked from commit 34bed3e36a05b8281b6248fc9a1340bd0f1828a8)