Deny updates to AWS::EC2::VolumeAttachment

In accordance with AWS docs [1] AWS VolumeAttachment does not support
updates of any of its properties.

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

Change-Id: I6d79536c68bed60d9b86c662147e35a9b2da6c1c
Closes-Bug: #1340096
Merge "Deny updates to AWS::EC2::VolumeAttachment"