Feature/#574 look at httpclient cache key (#589)

* #574 consolidate some code, man the config stuff is a mess!

* #574 just use the downstream re route and the key for caching http clients

* #574 added benchmark, i was suprised to learn using a complex type was faster than a string in benchmark .net dictionary tests, hey ho probably dont have enough data in the type...

test/Ocelot.Benchmarks/Program.cs

@@ -7,6 +7,7 @@ namespace Ocelot.Benchmarks
         public static void Main(string[] args)
         {
             var switcher = new BenchmarkSwitcher(new[] {
+                    typeof(DictionaryBenchmarks),
                     typeof(UrlPathToUrlPathTemplateMatcherBenchmarks),
                     typeof(AllTheThingsBenchmarks),
                     typeof(ExceptionHandlerMiddlewareBenchmarks)