Add tests for inheritance of properties in clowder.yml file and via command

[JrGoodle]

Expected behavior

Values will be inherited correctly

Actual behavior

No observed issues, but after finding a number of bugs in this logic, it's clear that proper tests are needed

Environment

• clowder version: 2.4.0
• OS: macOS
• Python version: 3.6

[JrGoodle]

Actually use unit tests for validating that values are inherited correctly