[Bug] Allow spark job to run a country for which no checks are configured to run

Describe the bug Spark job fails if country is configured to run but no checks are configured to run in that country. This is not ideal in a scenario where you have country restricted checks but want to run a small group of checks on a small group of countries.

To Reproduce

1. add "countries": ["NZL"] to the PoolSizeCheck object in the configuration.json.
2. in the atlas-checks spark job command (IntegrityCheckSparkJob) configure the job to run on NZL and AUS.
3. The job will complete for NZL but will fail afterwards since the check is restricted to NZL.

Expected behavior Allow jobs to complete when the job tries to run in a country where there are no atlas checks configured to run.

@Bentleysb