Increase support for the AllocationId property

This patch makes it possible to use the following snippet:

  "VpcIp": {
    "Type": "AWS::EC2::EIP",
    "Properties": {
      "Domain":"vpc"
    }
  },
  "VpcIPAssoc" : {
    "Type" : "AWS::EC2::EIPAssociation",
    "Properties" : {
       "InstanceId" : { "Ref" : "Server"},
       "AllocationId" : { "Ref" : "VpcIp" }
     }
  }

Previously the Heat service would fail the stack creation because it was
looking for the Neutron router created by means of AWS::EC2::VPC
resource.

Fixes bug: 1234671
Change-Id: I6fb6a5cd0d034d15516fcc0cb266c695836d972c
Merge "Increase support for the AllocationId property"