osd: Display scheduler specific info when dumping an OpSchedulerItem

osd: Display scheduler specific info when dumping an OpSchedulerItem

Implement logic to dump information relevant to the scheduler type being
employed when dumping details about an OpSchedulerItem. For e.g., the
'priority' field is relevant for the 'wpq' scheduler, but for the
'mclock_scheduler', the 'qos_cost' gives more information during debugging.

A couple of additional fields called 'qos_cost' and 'is_qos_request' are
introduced in OpSchedulerItem class. These are mainly used to facilitate
dumping of relevant information depending on the scheduler type. The
interesting points are when an item is enqueued and dequeued.

For the 'mclock_scheduler', the 'class_id' and the 'qos_cost' fields are
dumped during enqueue and dequeue op respectively. For the 'wpq' scheduler
things remain the same as before.

An additional benefit of this change is to help immediately identify the
type of scheduler being used for a given shard depending on what is dumped
in the debug messages while debugging.

Signed-off-by: Sridhar Seshasayee <sseshasa@redhat.com>