fix(get_docker_image_by_version): make it more roubst to errors

In some runs that are using AMIs which doesn't have corresponding
docker images, we've seen this failures, when c-s stress command
is running:

```
File "../sdcm/stress_thread.py", line 173, in _run_cs_stress
    cassandra_stress = get_docker_image_by_version(
        self.node_list[0].get_scylla_binary_version())
  File "../sdcm/utils/version_utils.py", line 354, in get_docker_image_by_version
    for image in all_tags['results']:
KeyError: 'results'
```

improved `get_docker_image_by_version` to be more robust on handling
errors, and melformed responses.

sdcm/utils/version_utils.py

@@ -349,14 +349,17 @@ def get_docker_image_by_version(scylla_version: str):
         scylla_version = short_scylla_version
 
     for page_number in count(start=1):
-        all_tags = requests.get(url=f'https://hub.docker.com/v2/repositories/{docker_repo}/'
-                                    f'tags?page_size=50&page={page_number}').json()
-        for image in all_tags['results']:
-            if scylla_version == image['name']:
-                return f"{docker_repo}:{image['name']}"
+        try:
+            all_tags = requests.get(url=f'https://hub.docker.com/v2/repositories/{docker_repo}/'
+                                        f'tags?page_size=50&page={page_number}').json()
+        except requests.RequestException:
+            break
+        for image in all_tags.get('results', []):
+            image_name = image.get('name')
+            if image_name and scylla_version == image_name:
+                return f"{docker_repo}:{image_name}"
         if not all_tags.get('next'):
             break
-
     # if image wasn't found, default to the latest releases
     return default_image
 

unit_tests/test_version_utils.py

@@ -2,8 +2,10 @@
 
 import os
 import unittest
+from unittest import mock
 
 import pytest
+import requests
 
 import sdcm
 from sdcm.utils.version_utils import (
@@ -412,3 +414,25 @@ def test_get_docker_image_by_version(version, expected):
 def test_get_docker_image_by_version_broken_string_version():
     with pytest.raises(AssertionError):
         get_docker_image_by_version(scylla_version="broken_version")
+
+
+def test_get_docker_image_by_version_fallback_on_errors():
+    def mock_requests_factory(response_stub):
+        return mock.Mock(**{
+            'json.return_value': response_stub,
+        })
+
+    def raise_request_error(**kwargs):
+        raise requests.HTTPError()
+
+    non_existing_version = '5.2.0~dev-0.20221124.999b7f5d9b77'
+    expected_fallback = 'scylladb/scylla:latest'
+    with unittest.mock.patch("requests.get") as get_mock:
+        get_mock.side_effect = lambda **_: mock_requests_factory({})
+        assert get_docker_image_by_version(scylla_version=non_existing_version) == expected_fallback
+
+        get_mock.side_effect = lambda **_: mock_requests_factory({"results": [{'name': ''}, {}]})
+        assert get_docker_image_by_version(scylla_version=non_existing_version) == expected_fallback
+
+        get_mock.side_effect = raise_request_error
+        assert get_docker_image_by_version(scylla_version=non_existing_version) == expected_fallback