Work around issue on frozen set generation

This is the sole solution i've managed to make build successfully images.

Refs. swh/infra/sysadm-environment#4724

scripts/app_manager.py

@@ -99,6 +99,14 @@ def generate_requirements_frozen(app: str, absolute_apps_dirpath: Path) -> None:
             f"{requirements} file for app {app} not found (checked {src_req_file})"
         )
 
+    def sanitize(requirements_content: bytes) -> bytes:
+        """Work around issue with wheel generating wrong version for pkg_resources."""
+        # Work around the virtualenv packaged in debian. By default, virtualenv will use
+        # shipped wheel from debian (which hold faulty dependency on
+        # pkg-resource=0.0.0). Hence creating issue when generating frozen deps set
+        # https://bugs.launchpad.net/ubuntu/+source/python-pip/+bug/1635463
+        return requirements_content.replace(b'pkg_resources==0.0.0\n', b'\n')
+
     with tempfile.TemporaryDirectory(prefix=app) as envdir:
         builder = AppEnvBuilder.bootstrap_venv(envdir)
 
@@ -106,7 +114,7 @@ def generate_requirements_frozen(app: str, absolute_apps_dirpath: Path) -> None:
         freeze_output = builder.run_pip("freeze", capture_output=True)
 
         with tempfile.NamedTemporaryFile(mode="wb", dir=app_dir, delete=False) as f:
-            f.write(freeze_output.stdout)
+            f.write(sanitize(freeze_output.stdout))
             p = Path(f.name)
             p.chmod(0o644)
             p.rename(dst_req_file)