Attach failure handlers on a per-request basis
Attach failure handlers on a per-request basis

Previously we affected the whole (shared) HttpClient; now we only attach the handler to the single HTTP request it's intended for.

Fixes #1430.

jskeet/google-api-dotnet-client,jskeet/google-api-dotnet-client,jskeet/google-api-dotnet-client,googleapis/google-api-dotnet-client,googleapis/google-api-dotnet-client,googleapis/google-api-dotnet-client