DB scripts: Add region to aws command, use python instead of python3

[rstorey]

Still need to make a couple more changes before this is ready:

• make ENV_NAME come from outside so it's set by the CloudFormation template rather than at the top of the script
• add region to the restore script

[coveralls]

Coverage increased (+0.03%) to 69.67% when pulling e5b2f9a on update-db-scripts into 5229350 on master.

[acdha]

+1 on this. If we wanted to be pedantically proper about this we could scrape the region into AWS_DEFAULT_REGION from the EC2/ECS instance metadata but I think we can way until it's deployed in n > 1 regions before caring about that.