Don't set the value for run_start until we actually receive...

...a run status packet.

Refs #6424
Use Poco::ScopedLock instead of explicit lock/unlock calls

Refs #6488
Use a mutex to protect access to run properties

The live listener has multiple threads that modify an event workspace.
It already uses a mutex to protect access to the workspace, but one
thread was modifying properties on that workspace without locking the
mutex.

Refs #6536