feat: forward application exit status

[mpolitzer]

After reviews, no change is required here ...

Exit with success:

cartesi-machine.lua -- true

         .
        / \
      /    \
\---/---\  /----\
 \       X       \
  \----/  \---/---\
       \    / CARTESI
        \ /   MACHINE
         '


Halted
Cycles: 36366527

Exit with "Nothing to do" is the same as success:

cartesi-machine.lua

         .
        / \
      /    \
\---/---\  /----\
 \       X       \
  \----/  \---/---\
       \    / CARTESI
        \ /   MACHINE
         '

Nothing to do.

Halted
Cycles: 33157931

Exit with failure:

cartesi-machine.lua -- false

         .
        / \
      /    \
\---/---\  /----\
 \       X       \
  \----/  \---/---\
       \    / CARTESI
        \ /   MACHINE
         '

[    0.198528] reboot: Restarting system with command '1'

Halted with payload: 1
Cycles: 35773807

Exit with an invalid code:

cartesi-machine.lua --append-rom-bootargs='single=yes' -- xhalt something_invalid

         .
        / \
      /    \
\---/---\  /----\
 \       X       \
  \----/  \---/---\
       \    / CARTESI
        \ /   MACHINE
         '

[    0.202688] reboot: Restarting system with command 'something_invalid'

Halted with payload: 4294967296
Cycles: 36340263

close #55

[mpolitzer]

No change needed here to support this feature