Add tests for openid signup with every provider

The spec for omniauth doesn't test signup for every provider, and it
doesn't test if it has tests for all available providers
Also, we no longer use secrets

* Add model test to check if the omniauth providers have changed
* Test signup using every provider
* Replace secretswith environment variables

spec/models/user_spec.rb

@@ -426,4 +426,10 @@ describe User do
       expect(user.events_registrations).to eq [@events_registration1, @events_registration2]
     end
   end
+
+  describe '.omniauth_providers' do
+    it 'contains providers' do
+      expect(User.omniauth_providers).to eq [:suse, :google, :facebook, :github]
+    end
+  end
 end