Error with auto discovery

[Nyholm]

Q	A
Bug?	yes
New Feature?	no
Version	dev-master

Actual Behavior

ServiceCircularReferenceException: Circular reference detected for service "httplug.auto_discovery.auto_discovered_client", path: "httplug.auto_discovery.auto_discovered_client".

Steps to Reproduce

httplug:
  clients:
    curl:
      factory: 'httplug.factory.curl'
      http_methods_client: true

HttpClientDiscovery::find();

To fix this PR

I added a failing test for this issue. Please make a PR to branch issue-188