Move size update to Cinder volume

In order to align AWS compatible Volume resource with current AWS
behavior [1], this patch moves volume size extension to the native Cinder
Volume resource.

[1] http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-ec2-ebs-volume.html

Change-Id: Ie1410d98175e1e42a95ca0fba72c48ca643a0dc7
Partial-Bug: #1340093