If backup drive is getting too full then remove backup directory before creating new backup

src/freedombone-backup-local

@@ -90,11 +90,16 @@ function make_backup_directory {
 function check_storage_space_remaining {
     # Check space remaining on the usb drive
     used_percent=$(df -k $USB_MOUNT | tail -n 1 | awk -F ' ' '{print $5}' | awk -F '%' '{print $1}')
-    if [ "$used_percent" -gt 95 ]; then
-        echo $"Less than 5% of space remaining on backup drive"
-        umount $USB_MOUNT
-        rm -rf $USB_MOUNT
-        exit 4
+    if [ "$used_percent" -gt 80 ]; then
+        echo $"Less than 20% of space remaining on backup drive"
+        if [ -d $USB_MOUNT/backup ]; then
+            echo $"Deleting existing backup directory"
+            rm -rf $USB_MOUNT/backup
+        else
+            umount $USB_MOUNT
+            rm -rf $USB_MOUNT
+            exit 4
+        fi
     fi
 }