Add minimum diskspace for curate_cache
Add minimum diskspace for curate_cache

==== Fixed Issues ====
#1141

====  Tech Notes ====
Curate cache now only removes cache files if the diskspace is below the
set percentage AND if below a set amount of free disk space

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