Allow web actions to respond with non-standard status codes

[Rodric Rabbah <ro...@gmail.com>]

I opened an issue https://github.com/apache/openwhisk/issues/5146 to
describe an issue we encountered with an enterprise client where web
actions returning some non standard HTTP status codes fail.

I think we can widen the handling of the status codes in the web actions
handler by first doing the int to code conversion from the action's
statusCode to a known value (as is done now), trapping any exceptions that
occur and then creating a custom status code on demand.

Looking through the akka library, I don't readily see a query method (to
check if the int to code conversion will pass) but will look through the
library a bit more.

Any objections to this enhancement?

-r