Indicate if profiling upload failed

[coreylight]

At times getting the error: "Download profiling data => "The specified key does not exist.""
https://iopipe.slack.com/archives/C6Q4HSLKD/p1518276447000024

Profiler should indicate if upload failed, so that there are no file misses.

[ewindisch]

The upload may fail for an object but our API does not know this as it bases the presence of profiling data based on if the plugin is enabled or not.

Two solutions are apparent to me:

• Mark the profiler as disabled if the profile upload fails
• Indicate in the data that the upload filed, but that the plugin was enabled.

I do not like the first solution as it does not allow us to detect failures, it would only remove visibility of the existence of an error.

With moving to using JWTs for uploading profile links, we can simply not include the JWT link if we know the upload to have failed. Consuming applications would have to be aware of this behavior and provide clean messages/warnings/errors around enabled profilers without uploads.