tests: add tests for setup-env.sh

- tests use a shell-script harness and test all Spack commands that
  require special shell support.

- tests work in bash, zsh, and dash

- run setup-env.sh tests on macos and linux builds.
  - we run them on macos and linux

.codecov.yml

@@ -11,5 +11,7 @@ ignore:
   - lib/spack/spack/test/.*
   - lib/spack/docs/.*
   - lib/spack/external/.*
+  - share/spack/qa/.*
+  - share/spack/spack-completion.bash
 
 comment: off