Added boto_cfn.py for beginning of Cloud Formation module

This is the very beginning of the Cloud Formation module, but it has been tested
and currently has the capability to create, delete, get_template, and test to
see if a Cloud Formation stack exists.  There are many more parts to be added,
but this will allow for Salt to create stacks.  As with all boto modules, this
can use credentials in the minion, pillar, or AWS IAM roles.  Not all methods
were tested, but it uses the same methods as other modules, and in fact was
created by just copying the SQS module and replacing most parts.
Merge branch 'cloud-formation' of https://github.com/freimer/salt into freimer-cloud-formation
lint, remove unused imports
Merge pull request #18607 from thatch45/freimer-cloud-formation

Merge #18555