Werk #8861: DCD: Gracefully handle single host issues when creating hosts

When one of multiple hosts could not be created or modified by a execution, this resulted in a complete termination of the execution. A persistent issue could totally break a connection, since no further steps would be executed.

As first step the "add_hosts" and "edit_hosts" API call has been extended to report back the result of a call. The structure looks like this:

{
    "succeeded_hosts": ["host1", "host3"],
    "failed_hosts": {
        "host2": "an error occured ...",
    },
}

The DCD reads this response and logs the result. In case there have been hosts added, the discovery is performed for them. After that, the connection continues with the following steps.

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