Document internet gateway properties:

AWS::EC2::VPCGatewayAttachment

Fixes bug #1224143

Change-Id: Ia896369f4cfcd5d13d66a2defb120b1c05d71fb6
api ec2token: Clear failure when no auth_uri specified

Currently if the CFN API is misconfigured, such that no auth_uri
is set in the config, we silently fail because we don't detect that
auth_uri==None in the code.  Instead catch this situation and assert
that the service is misconfigured via a 500 response.

Change-Id: I47a385aa6a34fe3133de00cf2b18fec6a4f6645a
Partial-Bug: #1229674
Merge "api ec2token: Clear failure when no auth_uri specified"
Merge "Document internet gateway properties:"