Fix error code 20 when doing msm default
Fix error code 20 when doing msm default

When running `msm default` the expected error code 20 (skill is already
installed) is always reported (unless the skills directory is empty).
This commit supressess that error to not confuse any users.

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