add debugging stats for high cpu usage

In cbstats 'raw workload' we record number of tasks that are
ready and number of sleeping threads
Change-Id: I82d595fcc1d2954963be4072d1c212556d91a136
Reviewed-on: http://review.couchbase.org/38909
Reviewed-by: abhinav dangeti <abhinav@couchbase.com>
Tested-by: Sundararaman Sridharan <sundar@couchbase.com>