Define region so CLI uses correct endpoint for localzones

[cartermckinnon]

Issue #, if available:

This is caused by a CLI bug: aws/aws-cli#7043

Description of changes:

When the CLI is used in a localzone; it constructs the wrong endpoint URL and the describe-instances call will always fail, such as:

> aws ec2 describe-instances --instance-ids i-0449a527fa4347213

Could not connect to the endpoint URL: "https://ec2.us-west-2-lax-1.amazonaws.com/"

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

Testing Done

The above failure is resolved by adding the --region flag. Tested on an instance in a local zone.