check execution on item when determining GetSSMParam task to use

[RobBrazier]

Issue #, if available:

Description of changes:
Check the execution defined on the launch/stack etc. as well as the global execution_mode

I'm not sure if the hasattr check is required, however as this is defined in child classes I thought it would be safer, happy to remove though

Currently as execution_mode is checked, within the spoke CodeBuild job of the puppet account, hub products are being launched and are failing to retrieve the SSM parameters as they have not been previously cached.

This worked previously when self.execution = "hub" and parameter_is_in_hub = True, as it will have gone into the standard GetSSMParamTask

However now that self.execution_mode is checked, when a hub product is processed, self.execution_mode = "spoke" and parameter_is_in_hub = True, so it'll drop into GetSSMParamFromManifestTask

I'm going to look through the logs to confirm whether the hub products were actually being launched before.

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[RobBrazier]

i'm not sure whether there's an environment issue - make install works fine when I run it locally, I did see a similar issue pypa/setuptools#2775 that's been around recently - I'm running python 3.9, wonder if it's related to 3.7?

[eamonnfaherty]

I have spotted the same issue. it has broken the coverage reporting. I have to move off python 3.7. I am hoping to get that done next week.