Fixed few subtle threading bugs uncovered by stress test and rewrote the test to be model-based (#1157)

* testing: refactored logs directory management

* content: fixed index mutex to be shared across all write sessions

added mutex protection during writecontent/refresh race

* testing: upload log artifacts

* content: bump revision number after index has been added

This fixes a bug where manifest manager in another session for
the same open repository may not see a content added, because they
will prematurely cache the incomplete set of contents.

This took 2 weeks to find.

* manifest: improved log output, fixed unnecessary mutex release

* testing: rewrote stress test to be model-based and more precise

.github/workflows/code-coverage.yml

@@ -18,3 +18,10 @@ jobs:
       run: make test-with-coverage
     - name: Publish Coverage Results
       run: make ci-publish-coverage
+    - name: Upload Logs
+      uses: actions/upload-artifact@v2
+      with:
+        name: logs
+        path: .logs/**/*.log
+        if-no-files-found: ignore
+      if: ${{ always() }}