AWS parameter type name instead of CFNType

[ejholmes]

Right now, if you want to specify a variable as a CloudFormation parameter, you would import the appropriate CFNType, then use that as the type field. For example:

from stacker.blueprints.variables.types import EC2VPCId

VARIABLES = {
    "VpcId": {
        "type": EC2VPCId
    }
}

This works fine, but I think we could make a little simpler and easier to use. If instead, you could do the following:

VARIABLES = {
    "VpcId": {
        "type": "AWS::EC2::VPC::Id"
    }
}

And stacker would internally convert it to a EC2VPCId. This behavior would be pretty similar to what we had in 0.8.