Scheduler: Reduce log level for non-configured projects

If Gerrit is hosting also projects that are not using this
Zuul instance it is annoying to get warnings about
non-configured projects for each received Gerrit event.
Therefore the log level is being reduced to debug.

Change-Id: I535a4f4778c1413b6d30f81980769128bbaba6db
Merge "Scheduler: Reduce log level for non-configured projects"