Unify retry logic and address download timeouts

[joelverhagen]

This is a continuation of #2057.

The failures that should be investigated are:

1. Errors while downloading the stream
   • Timeout (with Add download timeout to all network streams NuGet.Client#390)
2. Unify the retry logic. Right now, there is retries in:
   • HttpRetryHandler, for HTTP failures, timeouts and HTTP 500+
   • HttpFileSystemBasedFindPackageByIdResource
   • RemoteV2FindPackageByIdResource
   • DownloadResourceV3
   • Low priority: Authentication in HttpSource (user provided creds)
   • Low priority: Authentication in CredentialPromptWebRequestHandler (proxy authentication)
3. As many cases as possible should be unit testable (ideally all):
   • Low priority: Unify this test server with MockServer
4. Errors while fetching response
   • Low priority: Cannot reach DNS server (this could be really hard)
   • Low priority: SSL failure (bad trust)

Questions:

• The Throttle in HttpSource does not really throttle active HTTP session, since the lock is release before the response is disposed (e.g. the download is not done yet)

[yishaigalatzer]

Errors while downloading the stream

Is moving back for 3.4 RTM