Add support for use within AWS GovCloud

GovCloud does not have multiple zones (ATM) so I had to prevent the _get_region method from stripping off the last character in the zone. I got errors when setting the placement so I assume this parameter needs
to be ignored when in GovCloud. Last, boto needed to be upgraded to > 2.10.0 in order to support the new GovCloud region: https://github.com/boto/boto/blob/a47e0b8570ba7809dcc9c22f206ec9e0f9c14d9c/docs/source/releasenotes/v2.11.0.rst#features.