use to return this
return "arn:aws:cognito-identity:${{AWS::Region}}:${{AWS::AccountId}}:identitypool/{}".format(identity_pool_id)
now returns this
return "arn:aws:cognito-identity:{{{{REGION}}}}:{{{{ACCOUNT}}}}:identitypool/{}".format(identity_pool_id)
relieves the pain of debugging on the user end in cloudformation on why it doesn't work if they don't put it in Fn::Subs in the old version.