fix(test) - Reduce dependency on AWS config file

[kddejong]

Issue #, if available:

Description of changes:

• Current versions of tests rely on some information being in ~/.aws/config when doing mocks. This PR will completely remove that dependency.

You will have issues with the current version of the tests if you have no ~/.aws/config or are using the credential_process attribute in a profile

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[kddejong]

Waiting on #202

[kddejong]

Cross referencing this issue I raised with boto3 as I don't believe the credential_process should be executed on session.client or boto3.client call. More details on credential_process

boto/boto3#3456

[kddejong]

If no ~/.aws/config file exists

tests/lib/resource_test.py:92: AssertionError
------------------------------ Captured log call -------------------------------
ERROR    cloudformation_cli_python_lib.resource:resource.py:192 Exception caught You must specify a region.
Traceback (most recent call last):
  File "/root/cloudformation-cli-python-plugin/src/cloudformation_cli_python_lib/resource.py", line 207, in __call__
    metrics.add_metrics_publisher(provider_sess, event.resourceType)
  File "/root/cloudformation-cli-python-plugin/src/cloudformation_cli_python_lib/metrics.py", line 249, in add_metrics_publisher
    publisher = MetricsPublisher(session, type_name)
  File "/root/cloudformation-cli-python-plugin/src/cloudformation_cli_python_lib/metrics.py", line 39, in __init__
    self._client = session.client("cloudwatch")
  File "/usr/local/lib/python3.7/site-packages/boto3/session.py", line 309, in client
    config=config,
  File "/usr/local/lib/python3.7/site-packages/botocore/session.py", line 986, in create_client
    auth_token=auth_token,
  File "/usr/local/lib/python3.7/site-packages/botocore/client.py", line 136, in create_client
    auth_token,
  File "/usr/local/lib/python3.7/site-packages/botocore/client.py", line 481, in _get_client_args
    auth_token,
  File "/usr/local/lib/python3.7/site-packages/botocore/args.py", line 96, in get_client_args
    scoped_config,
  File "/usr/local/lib/python3.7/site-packages/botocore/args.py", line 192, in compute_client_args
    s3_config=s3_config,
  File "/usr/local/lib/python3.7/site-packages/botocore/args.py", line 284, in _compute_endpoint_config
    return self._resolve_endpoint(**resolve_endpoint_kwargs)
  File "/usr/local/lib/python3.7/site-packages/botocore/args.py", line 390, in _resolve_endpoint
    service_name, region_name, endpoint_url, is_secure
  File "/usr/local/lib/python3.7/site-packages/botocore/client.py", line 576, in resolve
    use_fips_endpoint=use_fips_endpoint,
  File "/usr/local/lib/python3.7/site-packages/botocore/regions.py", line 217, in construct_endpoint
    use_fips_endpoint,
  File "/usr/local/lib/python3.7/site-packages/botocore/regions.py", line 260, in _endpoint_for_partition
    raise NoRegionError()
botocore.exceptions.NoRegionError: You must specify a region.

[mmaeng]

LGTM

[kddejong]

big fan of stubber but haven't gotten it working with the mocked session. This also brings more consistency as these are the only tests using stubber.