Option to fix lambda name in settings.yml

[trecouvr]

It would like the option to fix my lambda names instead of gardon auto-generating it for me.

lambdas:
  helloworld:
    name: myAwesomeLambdaName
    runtime: nodejs6.10
    ..

I managed to hack gordon to pass the setting to troposphere.awslambda.Function and I can make a PR if you are interested.