Hard code /boot for root backups

Simplifies the configuration file and command line.
Signed-off-by: Robert Spencer <rspencer@lbsd.net>

scripts/backstep-traceback-auto

@@ -112,10 +112,9 @@ for lv in ast.literal_eval(config.get(PERIOD, "backup_lvs")):
     else:
         continue
 
-    if "," in lv:
-        lv, bind_mount = lv.split(",")
+    if lv == "root":
         bind_mount_args.append("--bind-mount")
-        bind_mount_args.append(bind_mount + ":" + bind_mount)
+        bind_mount_args.append("/boot:/boot")
 
     lvm_snapshot_args.append("--lvm-snapshot")
     lvm_snapshot_args.append(VG + "/" + lv)