Make reference leak detection more reliable
Make reference leak detection more reliable

The reference count sometimes reported that references were remaining
even if they actually weren't. By enforcing a garbage collector run
after shutting down a skill the false possitives are reduced if not
removed all together.

Dark5ide/mycroft-core,forslund/mycroft-core,MycroftAI/mycroft-core,linuxipho/mycroft-core,linuxipho/mycroft-core,forslund/mycroft-core,MycroftAI/mycroft-core,Dark5ide/mycroft-core