mocking around to make it safer

uboot.sh

test -n "${BOOT_ORDER}" || setenv BOOT_ORDER "A B"
test -n "${BOOT_A_LEFT}" || setenv BOOT_A_LEFT 3
test -n "${BOOT_B_LEFT}" || setenv BOOT_B_LEFT 3

setenv bootargs
for BOOT_SLOT in "${BOOT_ORDER}"; do
  if test "x${bootargs}" != "x"; then
    # skip remaining slots
  elif test "x${BOOT_SLOT}" = "xA"; then
    if test ${BOOT_A_LEFT} -gt 0; then
      setexpr BOOT_A_LEFT ${BOOT_A_LEFT} - 1
      echo "Found valid slot A, ${BOOT_A_LEFT} attempts remaining"
      setenv load_kernel "nand read ${kernel_loadaddr} ${kernel_a_nandoffset} ${kernel_size}"
      setenv bootargs "${default_bootargs} root=/dev/mmcblk0p1 rauc.slot=A"
      setenv rauc 1
    fi
  elif test "x${BOOT_SLOT}" = "xB"; then
    if test ${BOOT_B_LEFT} -gt 0; then
      setexpr BOOT_B_LEFT ${BOOT_B_LEFT} - 1
      echo "Found valid slot B, ${BOOT_B_LEFT} attempts remaining"
      setenv load_kernel "nand read ${kernel_loadaddr} ${kernel_b_nandoffset} ${kernel_size}"
      setenv bootargs "${default_bootargs} root=/dev/mmcblk0p2 rauc.slot=B"
      setenv rauc 1
    fi
  fi
done

if test -n "${rauc}"; then
  setenv rauc
  saveenv
  echo "Loading kernel"
  run load_kernel
  echo " Starting kernel"
  bootm ${loadaddr_kernel}
  reset
elif test -n "${bootargs}"; then
  saveenv
else
  echo "No valid slot found, resetting tries to 3"
  setenv BOOT_A_LEFT 3
  setenv BOOT_B_LEFT 3
  saveenv
  reset
fi

echo "Loading kernel"
run load_kernel
echo " Starting kernel"
bootm ${loadaddr_kernel}