Endless reprompting for credentials when invoking 'nuget push' with a bad APIKey

[claycompton]

This appears to be a regression in the current QA bits; I can't reproduce it in production.

To repro:

1. Create a package and push it to qa.nugettest.org using a bad API Key. In testing I used the following:

    nuget push -ApiKey fred C:\School\Bug1647\Bug1620.1.0.0.nupkg -Source https://qa.nugettest.org

1. You'll be prompted for a user name and password. Enter correct values for both.

Result: You'll be prompted for credentials again. This will continue ad infinitum.
Expected: I expect that any credentials check would report success or failure after the first try.

[analogrelay]

The issue appears to be that the Gallery used to respond with 403 Forbidden instead of 401 Unauthorized when it received a bad API Key. My vote is to fix this in the next dev sprint (i.e. not hold up our current deployment). But I will fix it.

[analogrelay]

(The fix is that we will use 403, because that is actually more appropriate. 401 indicates that the client can do something to authorize, 403 indicates that the client is simply unable to access the resource with the provided credentials)