910077: Removed offending Shutting down log statement.

Added text to each of the remaining Shutting down log entries which
result from an error during startup. The only one that print
Shutting down... alone is the shutdown hook which is the normal
shutdown mechanism for thumbslug.

Configuration error results int he following:
    "Unable to load config! Shutting down..."

Problem trying to daemonize:
    "Error during daemon initialization! Shutting down..."

Valid shutdown message:
    "Shutting down..."
Merge pull request #28 from candlepin/bz910077

910077: Removed offending Shutting down log statement.