Unspecified ErrorCode should say "UNSPECIFIED" instead of "UNAVAILABLE"

[NickKeller]

Feature Request

For clarity's sake, if the AzureError's response code is unspecified, the error message should say "ERROR CODE UNSPECIFIED", instead of what it currently does saying "ERROR CODE UNAVAILABLE". Since UNAVAILABLE is a legit http error code, it caused some confusion on my team when we were trying to debug an issue. I feel like it would be clearer to say "UNSPECIFIED", which is harder to mix up with an http error code

[chlowell]

Do you have an example confusing error? I'm wondering whether we have a bug that omits the status code, which should always appear on the first text line. For example:

--------------------------------------------------------------------------------
RESPONSE 500: it didn't work
ERROR CODE UNAVAILABLE
--------------------------------------------------------------------------------
error details from server
--------------------------------------------------------------------------------

So the HTTP status code should always appear before the RP's error code, if any

[NickKeller]

In this case the output is not due to the sdk, but we received output like this when checking for the status of an operation. We spent a while wondering why it would return a 200 with also "UNAVAILABLE".

Ultimately we figured out it was not an issue, but it would be a lot clearer if it had said "UNSPECIFIED". We spent quite a bit of time trying to figure out if the load balancer was overriding the status code to 200 when we thought the underlying service returned a 503, due to the UNAVAILABLE messaging

To be clear, there is no "bug" here, just a messaging issue, imo