Fix/consul poller option (#899)

* cache key now can generate from query string for request with Get Methods and request content for requests with post methods

* MD5Helper Added. OutputCacheMiddleware now can generate cache key using method, url and content

* ConsulFileConfigurationPollerOption created. consul poller option bug fixed

* ConsulFileConfigurationPollerOptionTest created

test/Ocelot.UnitTests/Configuration/FileConfigurationPollerTests.cs

@@ -126,6 +126,8 @@ namespace Ocelot.UnitTests.Configuration
                 .BDDfy();
         }
 
+        
+
         private void WhenProviderErrors()
         {
             _repo