Added us-gov-west-1 to list of choices

Minor updates to add us-gov-west-1 to the list of allowed choices. 

The `regions_exclude` still contains us-gov-west-1 in ec2.ini so it's still not included when selecting all regions. 

I was able to test this change and verify that it allows me provision and manage GovCloud EC2 instances after setting the `ec2_url` variable in my playbook.