Implement BlockDeviceMappings for AWS::EC2::Instance

We should support the BlockDeviceMappings for
AWS::EC2::Instance resource to be compatible with
AWSCloudFormation.

Implements blueprint implement-ec2instance-bdm

Change-Id: Ib4d318b429494f312f4d6978631dd0a9721b32ee
Merge "Implement BlockDeviceMappings for AWS::EC2::Instance"