ALBS-576: Notarize artifacts sequentially

See: https://github.com/codenotary/cas/issues/275

cas_wrapper.py

@@ -1,4 +1,3 @@
-from concurrent.futures import ThreadPoolExecutor, as_completed
 import json
 import logging
 import typing
@@ -166,15 +165,15 @@ class CasWrapper:
         all_artifacts_is_notarized = True
         notarized_artifacts = {}
         self.ensure_login()
-        with ThreadPoolExecutor(max_workers=4) as executor:
-            futures = {
-                executor.submit(self.notarize, artifact_path, metadata): artifact_path
-                for artifact_path in artifact_paths
-            }
-            for future in as_completed(futures):
-                artifact_path = futures[future]
+
+        # ALBS-576: We stopped doing this process in parallel due to the
+        # problems experienced and described in this CAS issue:
+        # https://github.com/codenotary/cas/issues/275
+        # Hence, we decided to go sequential here until the problem is
+        # resolved in CAS itself.
+        for artifact_path in artifact_paths:
             try:
-                    cas_artifact_hash = future.result()
+                cas_artifact_hash = self.notarize(artifact_path, metadata)
             except Exception:
                 self._logger.exception('Cannot notarize artifact: %s',
                                        artifact_path)