Unable to set stackId when testing with cfn invoke #998

When doing local testing of RESOURCEs, cfn invoke does not provide the ability to set a stackId on the request. This causes any handlers relying on the stackId to fail or incorporate special handling for missing stackId values.

Ideally, should be able to pass JSON like:

{
    "stackId": "test-stack",
    "desiredResourceState": {
        "Key1": "Value1",
        "Key2": "Value2"
    },
    "previousResourceState": {},
    "logicalResourceIdentifier": "SomeIdentifier"
}