HTTP Client failures case name and attributes conform to requirements

• Manual test: We try to hit a non-existent host.

   TranslationServiceSettings.Builder settingsBuilder = TranslationServiceSettings.newBuilder();
    
   settingsBuilder
	.getStubSettingsBuilder()
	.setEndpoint("non-existent:1234")
	.setTracerFactory(createOpenTelemetryTracerFactory());

• HTTP
  • 

  • Confirmed this 500 (UnknwonException) is part of unwrapping the exception (see related code). The actual code may not be desired but it respects the logic, so if a fix is wanted it should be done in gax-httpjson