SNSLiveEventDataListener: Reduce a warning from error to debug

[mantid-builder]

Original Reporter: Russell Taylor

In the testing of http://trac.mantidproject.org/mantid/ticket/8065 and subsequently, the log message at line 609 of SNSLiveEventDataListener has been observed:

g_log.error() << "run_number property already exists.  Current value will be ignored."  << std::endl
              << "(This should never happen.  Talk to the Mantid developers.)" << std::endl;

I think that this can now appear if the listener is started outside a run, or there is a gap between runs. A run number of 0 will be entered if a RunStatus::STATE packet is encountered. The message will then be seen when a new run starts. This situation should be avoided with the fixing of http://trac.mantidproject.org/mantid/ticket/7209.

In the meantime, logging this message at error level is not helpful - it is really a very minor issue (the run number will be wrong inside the workspace) and having it appear may concern some users unnecessarily.

[mantid-builder]

This issue was originally trac ticket 8289