Add validate function for AWS::EC2::EIPAssociation

This is second part of blueprint implement-ec2eip-updatable to
add validate function for AWS::EC2::EIPAssociation

Implements blueprint implement-ec2eip-updatable

Change-Id: I907eddef943a4ecf5c64f2358b6fd6a7e152497c
Merge "Add validate function for AWS::EC2::EIPAssociation"