Support functionName, functionVersion and invokedFunctionArn property on clientContext

[vamship]

Allow deployment of packages from an S3 bucket instead of always requiring an upload from the file system. This is useful in two scenarios:
(1) Package build is performed by a different process, but deployment has to be gated by some approval workflow
(2) Multiple lambda functions use the same code base - this requires multiple uploads of the exact same package, making the deployment quite slow.

This allows us to specify an optional values for functionName, functionVersion and invokedFunctionArn properties on the client context. These properties are described here: http://docs.aws.amazon.com/lambda/latest/dg/nodejs-prog-model-context.html.