Change cloud person username fields to be not null

[eiffel777]

In PR #797 the Person and System Account group bys were added to the Cloud realm. In that PR the person_id field was added to the staging tables with a default of NULL and was added to the Primary Key on that table. This caused the error below on the xdmod-dev database.

xdmod.jobs-cloud-extract-openstack.OpenStackCloudStagingEventIngestor (ETL\Ingestor\DatabaseIngestor): 
Error managing ETL table for 'xdmod.jobs-cloud-extract-openstack.OpenStackCloudStagingEventIngestor': 
SQLSTATE[42000]: Syntax error or access violation: 1171 All parts of a PRIMARY KEY must be NOT NULL; if you need NULL in a key, use UNIQUE instead

This error doesn't show up on metrics-dev or in the my docker but does on xdmod-dev and it seems to be because metrics-dev and my docker run MySQL 5.5 and xdmod-dev runs MySQL 5.7. It seems MySQL is stricter about errors in 5.7.

Changing the person_id definition to NOT NULL with a default of -1 fixes this.

Tests performed

Manually tested in docker and on xdmod-dev. All tests pass

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project as found in the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.