Nalu-Wind Submodules are not enabled unless branch is master

[psakievich]

@ndevelder @jrood-nrel trying to run tests with [email protected] fails because we don't enable submodules for any branch but master. We need to figure out how to conditionally turn them on. I know it can be done but we just need to do it. This will probably be something we need to add to spack core.