View source for Cinder count api

== Problem description ==
There is no current API that can retrieve summary count data for volumes and search filters.  For example, getting the total number of volumes that match a given filter criteria (for example, all volumes in a given state).  Retrieving all volumes and then manually determining the count data does not scale.
=== Use Case ===
A UI dashboard that contains volumes in various states.  A new API is needed to retrieve the volume count data associated with various filters (ie, volumes in available state, volumes in error state, etc.)