core: in confirm_spawn, the meaning of 'n' and 's' choices are confusing

core: in confirm_spawn, the meaning of 'n' and 's' choices are confusing

Before this patch we had:

 - "no" which gives "failing execution" but the command is actually assumed as
   succeed.

 - "skip" which gives "skipping", but the command is assumed to have failed,
   which ends up with "Failed to start ..." on the console.

Now we have:

 - "fail" which gives "failing execution" and the command is indeed assumed as
   failed.

 - "skip" which gives "skipping execution" and the command is assumed as
   succeed.