Check for node runtimes first

[smil2k]

webpack should not try to load handlers of different runtime than node.

What did you implement:

Closes #255 or #256, #535

How did you implement it:

How can we verify it:

This config will work:

provider:
  name: aws
  runtime: nodejs12.x 

functions:
  echo:
    handler: lambda.echo
    events:
      - http:
          path: /api/echo2
          method: any
  all:
    handler: backend.lambda.LambdaFunction
    runtime: java8
    events:
      - http:
          path: /api/v1/{api+}
          method: any     

Todos:

• Write tests
• Write documentation
• Fix linting errors
• Make sure code coverage hasn't dropped
• Provide verification config / commands / resources
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: YES
Is it a breaking change?: NO

[miguel-a-calles-mba]

Please add unit tests.

[j0k3r]

@miguel-a-calles-mba I think tests from #530 should be ported here (and then closed) and that PR be merged instead oh the other one (because it handles the global runtime)

[miguel-a-calles-mba]

Works for me @j0k3r. I updated the test.