mac: mitigate "device busy" chances when ejecting DMG

tools/osx_packaging/osx_build

@@ -1088,6 +1088,7 @@ fi
 
 osascript << EOF
   tell application "Finder"
+    close every window
     activate
     tell disk "${DISKNAME}"
       open
@@ -1126,6 +1127,8 @@ EOF
 
 chmod -Rf go-w "${MNTPATH}"
 sync
+sleep 1
+sync
 
 set -e
 echo "compressing Image ..."