Refactor gator test's pkg/ files into their own sub-package

[julianKatz]

Currently, the pkg/gator package holds all the code for gator test. With the addition of the gator test command, this structure will no longer make sense.

As part of this issue, complete the following:

• Create a pkg/gator/test package that holds the most test specific functionality.
• Update cmd/gator/test to use the new package
• Move the ToTemplate function (or something like it) into a shared util.go at pkg/gator
• Update pkg/gator/validate to use that new package

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 14 days if no further activity occurs. Thank you for your contributions.

[julianKatz]

Still a good idea

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 14 days if no further activity occurs. Thank you for your contributions.

[davis-haba]

I think we can close this once #2398 is merged. This PR included a big refactor of the Gator CLI to break up commands into their own subpackages.