crimson/osd,osd_operation: initialize mClock scheduler, detect rotational devices...

crimson/osd,osd_operation: initialize mClock scheduler, detect rotational devices, and run OperationThrottler background task

Initialize the mClock scheduler on all shards when the device class
is non-rotational. If the device is rotational throw an exception
to prevent unsupported configurations.

In addition, introduce a background task in OperationThrottler that
continuously dequeues and schedules client requests from the mClock
scheduler based on available credits and throttling limits.

Signed-off-by: Mohit Agrawal <moagrawa@redhat.com>