Publish coverage on coveralls in gh workflow (WIP)

Does not work yet!

TODO:
Troubleshoot
- Official coveralls action does not seem to work well for Python
  coverallsapp/github-action#4
  coverallsapp/github-action#30
- Inofficial coveralls action seems to correctly talk to the API
  but has issues finding the coverage data in the tests folder,
  or rather the corresponding code.
  https://github.com/AndreMiras/coveralls-python-action
- Official coveralls cli tool (see travis) triggers 500 on coveralls.io

.github/workflows/ci.yml

@@ -12,18 +12,20 @@ jobs:
       # Run regular TUF tests on each OS/Python combination, plus special tests
       # (sslib master) and linters on Linux/Python3.x only.
       matrix:
-        python-version: [2.7, 3.6, 3.7, 3.8, 3.9]
-        os: [ubuntu-latest, macos-latest, windows-latest]
+        # python-version: [2.7, 3.6, 3.7, 3.8, 3.9]
+        python-version: [3.9]
+        # os: [ubuntu-latest, macos-latest, windows-latest]
+        os: [ubuntu-latest]
         toxenv: [py]
-        include:
-          - python-version: 3.x
-            os: ubuntu-latest
-            toxenv: with-sslib-master
-            experimental: true
-          # TODO: Change to 3.x once pylint fully supports Python 3.9
-          - python-version: 3.8
-            os: ubuntu-latest
-            toxenv: lint
+        # include:
+        #   - python-version: 3.x
+        #     os: ubuntu-latest
+        #     toxenv: with-sslib-master
+        #     experimental: true
+        #   # TODO: Change to 3.x once pylint fully supports Python 3.9
+        #   - python-version: 3.8
+        #     os: ubuntu-latest
+        #     toxenv: lint
 
     runs-on: ${{ matrix.os }}
 
@@ -53,7 +55,29 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          python -m pip install tox
+          python -m pip install tox coveralls
 
       - name: Run tox
-        run: tox -e ${{ matrix.toxenv }}
+        run: |
+          tox -e ${{ matrix.toxenv }}
+          cat tests/.coverage
+          pwd
+
+  #     - name: Publish coverage
+  #       if: matrix.toxenv == 'py'
+  #       uses: AndreMiras/coveralls-python-action@v20201129
+  #       with:
+  #         flag-name: ${{ runner.os }} / Python ${{ matrix.python-version }}
+  #         parallel: true
+  #         debug: true
+  #         base-path: '.'
+
+  # finish:
+  #   needs: build
+  #   runs-on: ubuntu-latest
+  #   steps:
+  #     - name: Publish coverage (fin)
+  #       uses: AndreMiras/coveralls-python-action@v20201129
+  #       with:
+  #         parallel-finished: true
+  #         debug: true

tests/.coveragerc

@@ -1,5 +1,6 @@
 [run]
 branch = True
+relative_files = True
 
 omit =
     # Command-line scripts.