Differentiate thick and thin provisioning logic in scheduler

Currently in the capacity filter and weigher of the scheduler, we use the the logic to evaluate whether there is enough capacity to thin provision a volume on a backend if the driver reports thin_provisioning_support to be True. However, a driver may be able to support both thin and non-thin provisioning. The logic does not check whether the user wants the volume to be provisioned as thin or not. This blueprint proposes to fix the problem by checking 'thin_provisioning_support' in extra specs of the volume type.