Set exit code when commands fail

If I run git node land on a new machine with nothing configured, I'll get the instructions to set required variables, and then the process will exit with status code 0. In order for us to be able to use ncu on a Commit Queue, it needs to return the appropriate status codes when something goes wrong, otherwise automation won't work.

(I didn't check which other failures will exit with 0, but all failures should set the exit code to a non-zero code)

Empieza reproduciendo git node land en una máquina nueva con las variables requeridas sin establecer y, a continuación, rastrea cómo termina el fallo. Revisa las rutas de comandos de ncu que informan de errores; se considera terminado cuando los fallos devuelven códigos de estado distintos de cero para que la automatización de Commit Queue pueda detectarlos.