Region from Env Vars or profile are not respected for ALL commands but package and deploy

[jfuss]

The region option in SAM CLI was changed between 0.7.0 and 0.8.0 to add the default explicitly on the command line option. This causes the region to always be set and not allow boto3 to do its resolving of credentials and regions, which is used to set the correct values into the docker container.

Current workaround is to explicitly set the region when invoking a function or interacting with commands that interact with AWS Services.

Fix is in #811