vdk-core: termination message now idempotent

[mrMoZ1]

what: termination message plugin now overrides the previous message.

why: Some data jobs that make use of the Standalone Data Job end up with double termination message, e.g.,

'{"vdk_version": "0.3.572339461", "status": "Success"}{"vdk_version": "0.3.572339461", "status": "Success"}'

This confuses the Control Service, which therefore classifies the execution as Platform Error, even if the job is executed successfully.

testing: added unit tests

Signed-off-by: Momchil Zhivkov [email protected]

[ivakoleva]

Not sure ifidempotence is the word to use, the data job remains the same yet multiple different statuses are written sequentially during execution, yes?
Where in the workflow is the written status used?

[ivakoleva]

If hook implementations have to be idempotent, the API docs should be clearly stating this. Does the API contract the idempotent implementation, or not?

I saw the idempotent hook implementation was a suggestion made, so I am unblocking the MR.