Enable connect_to_region('us-gov-west-1') for all services in GovCloud

added region information to the __init__.py for each service

additional updates supporting govcloud functionality:
- update auth.py HmacAuthV4Handler to return the correct region name
- update iam/connection.py to return the correct IAM signin url for govcloud
add unit test coverage for HmacAuthV4Handler.credential_scope()

validate two existing use cases with iam.amazonaws.com and
iam.us-gov.amazonaws.com as well as the potential use case of
iam.<some-region>.amazonaws.com with the non-existant
iam.us-west-1.amazonaws.com
Enable connect_to_region(us-gov-west-1) for vpc services in GovCloud
Merge remote-tracking branch 'carllen/connect_to_region_us-gov-west-1' into develop