Make GHA tests parallel by using xdist (#32361)

* Add two no-op jobs named "all-prechecks" and "all"

These are a suggestion from @tgamblin, they are stable named markers we
can use from gitlab and possibly for required checks to make CI more
resilient to refactors changing the names of specific checks.

* Enable parallel testing using xdist for unit testing in CI

* Normalize tmp paths to deal with macos

* add -u flag compatibility to spack python

As of now, it is accepted and ignored.  The usage with xdist, where it
is invoked specifically by `python -u spack python` which is then passed
`-u` by xdist is the entire reason for doing this.  It should never be
used without explicitly passing -u to the executing python interpreter.

* use spack python in xdist to support python 2

When running on python2, spack has many import cycles unless started
through main.  To allow that, this uses `spack python` as the
interpreter, leveraging the `-u` support so xdist doesn't error out when
it unconditionally requests unbuffered binary IO.

* Use shutil.move to account for tmpdir being in a separate filesystem sometimes

.github/workflows/audit.yaml

@@ -0,0 +1,44 @@
+name: audit
+
+on:
+  workflow_call:
+    inputs:
+      with_coverage:
+        required: true
+        type: string
+      python_version:
+        required: true
+        type: string
+
+concurrency:
+  group: audit-${{inputs.python_version}}-${{github.ref}}-${{github.event.pull_request.number || github.run_number}}
+  cancel-in-progress: true
+
+jobs:
+  # Run audits on all the packages in the built-in repository
+  package-audits:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # @v2
+    - uses: actions/setup-python@b55428b1882923874294fa556849718a1d7f2ca5 # @v2
+      with:
+        python-version: ${{inputs.python_version}}
+    - name: Install Python packages
+      run: |
+        pip install --upgrade pip six setuptools pytest codecov 'coverage[toml]<=6.2'
+    - name: Package audits (with coverage)
+      if: ${{ inputs.with_coverage == 'true' }}
+      run: |
+          . share/spack/setup-env.sh
+          coverage run $(which spack) audit packages
+          coverage combine
+          coverage xml
+    - name: Package audits (without coverage)
+      if: ${{ inputs.with_coverage == 'false' }}
+      run: |
+          . share/spack/setup-env.sh
+          $(which spack) audit packages
+    - uses: codecov/codecov-action@81cd2dc8148241f03f5839d295e000b8f761e378 # @v2.1.0
+      if: ${{ inputs.with_coverage == 'true' }}
+      with:
+        flags: unittests,linux,audits