Extension Configs

[Paul-Ferrell]

Extension configs would be like normal Pavilion configs, but would layer differently.

• Extensions would be applied after modes.
• List values in extensions would be prepended to existing lists.

That's actually it, basically. Extensions would be a non-modifiable key in the tests themselves - they are applied before variables are resolved.

Multiple extensions should also be a consideration - if two extensions modify {{sched.test_cmd}} only the second would normally apply. Maybe modify such that the extension of that variable list references each successive list item or something.