Check empty array before terminating/deleting (aws-observability#147)

*Issue description:*
Check empty array before deleting ASGs or terminating instances in
resource clean up to avoid errors:
```
Error terminating instances: An error occurred (InvalidParameterCombination) when calling the TerminateInstances operation: No instances specified
```

*Description of changes:*

*Ensure you've run the following tests on your changes and include the
link below:*
To do so, create a `test.yml` file with `name: Test` and workflow
description to test your changes, then remove the file for your PR. Link
your test run in your PR description. This process is a short term
solution while we work on creating a staging environment for testing.

NOTE: TESTS RUNNING ON A SINGLE EKS CLUSTER CANNOT BE RUN IN PARALLEL.
See the
[needs](https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idneeds)
keyword to run tests in succession.
- Run Java EKS on `e2e-playground` in us-east-1 and eu-central-2
- Run Python EKS on `e2e-playground` in us-east-1 and eu-central-2
- Run metric limiter on EKS cluster `e2e-playground` in us-east-1 and
eu-central-2
- Run EC2 tests in all regions
- Run K8s on a separate K8s cluster (check IAD test account for master
node endpoints; these will change as we create and destroy clusters for
OS patching)

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license.

.github/workflows/resource-cleanup.yml

@@ -45,7 +45,7 @@ jobs:
           role-to-assume: arn:aws:iam::${{ env.ACCOUNT_ID }}:role/${{ secrets.RESOURCE_CLEANER_ROLE_NAME }}
           aws-region: ${{ matrix.aws-region }}
 
-      - name: Cleanup EC2 instances
+      - name: Cleanup EC2 instances and ASGs
         working-directory: .github/workflows/util/clean/ec2_instance_cleanup
         env:
           AWS_DEFAULT_REGION: ${{ matrix.aws-region }}

.github/workflows/util/clean/ec2_instance_cleanup/cleaner.py

@@ -66,7 +66,7 @@ def _delete_autoscaling_groups(auto_scaling_groups):
             logging.info("===== Response for delete autoscaling group request =====")
             logging.info(response)
         except Exception as e:
-            logging.info(f"Error terminating instances: {e}")
+            logging.info(f"Error deleting groups: {e}")
 
 def _is_active(asg):
     for instance in asg['Instances']:
@@ -191,13 +191,18 @@ def _terminate_instances(instances_to_terminate):
     instances = _get_instances_to_terminate()
 
     if len(groups) == 0 and len(instances) == 0:
-        logging.info("No resource to terminate")
+        logging.info("No resource to clean up")
         exit(0)
 
     report_successful = _prepare_report_and_upload(groups, instances)
     if not report_successful:
-        logging.error("Failed to prepare report and upload. Aborting termination of instances.")
+        logging.error("Failed to prepare report and upload. Aborting resource clean up.")
         exit(1)
 
-    _delete_autoscaling_groups(groups)
-    _terminate_instances(instances)
+    if len(groups) > 0:
+        logging.info("Deleting autoscaling groups...")
+        _delete_autoscaling_groups(groups)
+
+    if len(instances) > 0:
+        logging.info("Terminating instances...")
+        _terminate_instances(instances)