[SYSTENDS-3197] Federated Put variable overwrite

This commit fixes two issues in the federated worker handler

1. When executing multiple jobs with a single federated worker without
sending a clear command the PUT_VAR would not overwrite the previous value,
and make an error response that was not propergated to the caller.

2. If any command crash in the sequrnce of commands, the error would not
be returned to the caller if the last command succeed. This is common since
the last command usually was a EXEC_INST clear variable.

The fix is to return to the caller at the first error encountered.
And allow PUT_VAR to overwrite variable IDs, since we are not officially
supporting multi tenants, this is a safe assumption.

Also contained in this commit is some minor adjustments to the error
handling, to make the code cleaner, and the logging to terminals less.