Openwhisk: do not base64 encode __ow_body for raw web actions

[rabbah]

3919 removes the base64 encoding requirement when returning JSON as string (and setting the content-type). However we continue to encode JSON for raw http actions receiving __ow_body. For symmetry, we should stop doing that as well. This is largely in place for legacy reasons (spray vs akka). The net of this change is that functions would JSON.parse(param.__ow_body) instead of JSON.parse(decode64(param.__ow_body)).

[tripodsan]

this change will introduce backward compatibility issues, if you just change the encoding.
that is needed is a flag that indicates if the body is base64 encoded or not. eg: __ow_body_isbase64

[rabbah]

Indeed it would be backward incompatible. The flag is a great way to transition.