aursec-chain: proper error handling

[clawoflight]

Because of the complexity of the involved processes, it would be very helpful to handle some errors explicitly and give descriptive error messages:

• check exit statuses of critical commands
• parse the json response where applicable

[Lifree]

improved by https://github.com/clawoflight/aursec/commit/3d7664a6e63e6e5df78d6fc2f5aeeabf46da25e7 parsing json response will not be possible with the current traps

[Lifree]

Done by https://github.com/clawoflight/aursec/commit/47f39c18f3ed5b9a84cc1bd54a772d81e4516714