Add support for volume types with Generic driver

Add configuration option cinder_volume_type which can be used
to set volume type for cinder. If that option is not None then
cinder volumes will be created with type from that option.

Implements blueprint cinder-volume-types-with-generic-driver

Change-Id: Ica171410bfdfa001da5188450a0c3740b4b8eb65
Merge "Add support for volume types with Generic driver"