Fix Authorizer: NONE support with AWS_IAM authorizer

[TDaglis]

Issue #1014

Description of changes:
Change the validation of method_authorizer to support the combination of AWS_IAM default authorizer and NONE method authorizer.

When using AWS_IAM permission, it is only specified in the DefaultAuthorizer. Reference. This is a special case which leads to the api_authorizers being empty and results to not being able to add

Auth:
 Authorizer: 'NONE'

to a specific function, in order to override the default authorizer and make the function public.

Description of how you validated changes:

Checklist:

• Write/update tests
• make pr passes
• Update documentation
• Verify transformed template deploys and application functions as expected
• Add/update example to examples/2016-10-31

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

[praneetap]

Thanks for the PR! The Travis build is failing. Once those errors are fixed we will give this a deeper review.

[keetonian]

Ran tests locally and they all passed. Re-running travis.

[codecov-io]

Codecov Report

Merging #1015 into develop will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           develop    #1015   +/-   ##
========================================
  Coverage    94.81%   94.81%           
========================================
  Files           69       69           
  Lines         3276     3276           
  Branches       639      639           
========================================
  Hits          3106     3106           
  Misses          89       89           
  Partials        81       81

Impacted Files	Coverage Δ
samtranslator/model/eventsources/push.py	88.6% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 527c190...db1b887. Read the comment docs.

[jhaenchen]

I need this fix folks, just checking in!

[praneetap]

Thank you for the contribution! Could you please add end to end tests (Input/Output) that verifies the fix? You can take a look at this pr for guidance. Please make sure you follow the pr checklist.

[TDaglis]

I attempted to add an end to end test, but it appears that it has issues in Python2.7. I don't understand what the issue is exactly. Any direction on this would be helpful. I'll get back to it.

[TDaglis]

It appears my output files had issues with Python2.7. I fixed them and now the tests pass.