Bootstrap environment modules optimizing for generic architectures (#13105)

fixes #13073

Since #3206 was merged bootstrapping environment-modules was using the architecture of the current host or the best match supported by the default compiler. The former case is an issue since shell integration was looking for a spec targeted at the host microarchitecture.

1. Bootstrap an env modules targeted at generic architectures
2. Look for generic targets in shell integration scripts
3. Add a new entry in Travis to test shell integration