Full stack FDK tests

[denismakogon]

As for now, there's a need to run full stack tests on FDK:

1. Download the CLI (latest).
2. Download and start background Fn server.
3. Do tests that involve boilerplate generation for the following cases:

• simple hello-world
• response with headers
• context operations
• deadline manipulations.

[riconnon]

I'm not actually sure we do need this. We just need to test against the FDK contract. If eg. if Fn-Deadline is specified we should have the appropriate deadline.

[denismakogon]

There’s no way to test this within the FDK only, because we might have the problem we had with the deadline header. This type of things must be tested within the Fn + FDK. This type of test may help to catch the regression in the amount of time being consumed by Fn before starting the response listener (deadline header is a time stamp, but not the amount of seconds/minutes to wait until aborting a user’s call).