Add feature that administrators can get back-end storage pools
filtered by volume-type, Cinder will return the pools filtered
by volume-type's extra-spec. This is depended on generalized
resource filtering feature.
APIImpact
Depends-On: ff3d41b15abb2915de87830980147be51e5da971
Implements: blueprint add-volume-type-filter-to-get-pool
Change-Id: If2ae4616340d061db833cbbdffc77f3e976d8254