Create an integration test for "configuration reload" functionality

The integration test should use custom "validate" step that would:

* Save configs to "saved" directory
* Bring the lab down
* Restart the lab with "netlab up --snapshot --reload saved"
* Do the validation test

The easiest way to do multi-step validation would be to create a .sh file with the files plugin

Optional: custom "up" check that would check the "can reload" feature