Heavily comment the integration_test_lib and test_executive

[Isaac-DeFrain]

Problem
There are very few comments in the integration_test_lib. This makes the learning curve too steep.

Assessment Criteria
Commonly used testing functions will have numerous comments to aid test writers.

Tasks

• Add comments to Intf module values, types, modules, and signatures
• Add comments to Dsl module values, types, modules, and signatures
• Add comments to Test_config module values, types, modules, and signatures
• Add comments to Malleable_error module values, types, modules, and signatures
• Add comments to Test_common module

[Isaac-DeFrain]

WIP PR for Test_common and integration test improvements #18