Optionally remove existing usb backup before starting new one

src/freedombone-backup-local

@@ -189,6 +189,17 @@ function make_backup_directory {
     fi
 }
 
+function remove_backup_directory {
+    if [ $1 ]; then
+        if [[ $1 == "remove" ]]; then
+            if [ ! -d $USB_MOUNT/backup ]; then
+                rm -rf $USB_MOUNT/backup
+                echo 'Existing backup directory removed'
+            fi
+        fi
+    fi
+}
+
 function check_storage_space_remaining {
     # Check space remaining on the usb drive
     used_percent=$(df -k $USB_MOUNT | tail -n 1 | awk -F ' ' '{print $5}' | awk -F '%' '{print $1}')
@@ -324,6 +335,7 @@ function backup_directories {
 }
 
 mount_drive $1 $2
+remove_backup_directory $2
 make_backup_directory
 check_storage_space_remaining
 backup_users