fix busy waits in scheduler threads
fix busy waits in scheduler threads

aurelijusb/arangodb,nvoron23/arangodb,nekulin/arangodb,nvoron23/arangodb,aurelijusb/arangodb,aurelijusb/arangodb,nvoron23/arangodb,nvoron23/arangodb,aurelijusb/arangodb,aurelijusb/arangodb,nvoron23/arangodb,aurelijusb/arangodb,nvoron23/arangodb,aurelijusb/arangodb,nvoron23/arangodb,nekulin/arangodb,nekulin/arangodb,nekulin/arangodb,nekulin/arangodb,nvoron23/arangodb,aurelijusb/arangodb,aurelijusb/arangodb,nekulin/arangodb,nekulin/arangodb,nekulin/arangodb,nekulin/arangodb,nekulin/arangodb,nvoron23/arangodb,nvoron23/arangodb,aurelijusb/arangodb