Refactor util to create S3 buckets with location constraints

[whummer]

Minor refactoring in utils to create S3 buckets with location constraints. Buckets now need to be created with the correct region / location constraint (for parity with AWS).

We can use the create_s3_bucket(..) util function to simplify this task and streamline creation of buckets across the codebase. Intended to be used in places where we need to create temporary buckets for other services, e.g., in the case of CloudFormation, to avoid these exceptions:

localstack_main |     s3_client.create_bucket(Bucket=CUSTOM_RESOURCES_RESULTS_BUCKET)                                                                                                                                                                          
localstack_main |   File "/opt/code/localstack/.venv/lib/python3.8/site-packages/botocore/client.py", line 415, in _api_call                                                                                                                                  
localstack_main |     return self._make_api_call(operation_name, kwargs)                                                                                                                                                                                      
localstack_main |   File "/opt/code/localstack/.venv/lib/python3.8/site-packages/botocore/client.py", line 745, in _make_api_call                                                                                                                              
localstack_main |     raise error_class(parsed_response, operation_name)
localstack_main | botocore.exceptions.ClientError: An error occurred (IllegalLocationConstraintException) when calling the CreateBucket operation: The unspecified location constraint is incompatible for the region specific endpoint this request was sent t

[thrau]

LGTM!

[coveralls]

Coverage decreased (-0.2%) to 91.884% when pulling fe9ebb7 on util-create-bucket into b5d1dd3 on master.