gpexpand does not currently work with a ICW dump yet, so this commit
prepares for that step as we work to fix all the outstanding errors.

We have also made the following changes:

Refactor and cleanup gpexpand behave tests

Add gpexpand test that can be run locally

Add new gpexpand test to verify redistribution

Add initial gpexpand test using snowflake-simple-database until we fix
gpexpand ICW dump errors
Co-authored-by: NKalen Krempely <kkrempely@pivotal.io>
Co-authored-by: NShoaib Lari <slari@pivotal.io>