fix awscli patch for new create_nested_client, introduce bats tests

[alexrashed]

Motivation

awscli version 1.41.9 comes with aws/aws-cli#9602, which changes the way the AWS client is created. This conflicts with our patch for Cloudformation (modifying the S3 endpoint URL).
This PR fixes this, and also introduces a proper testing framework (bats).
Fixes #91.

Changes

• Introduces a new test pipeline which runs certain smoke tests using bats.
• Fixes the patch of the create_client function for awslocal cloudformation package and awslocal cloudformation deploy.
  • Instead of using a fixed position in the outer frames, we now backtrack to see if we can find the right frame in the whole set of frames. This approach is compatible with the versions before 1.41.9, as well as the versions since then.