LP#1284137: Avoid WARN logging on router shutdown

Log received signals as DEBUG (misc signal) or INFO (during shutdown)
in the router, since these are not error conditions, but normal
operations.

A warning may ultimately be logged at a higher level when the signal is
unexpected.

Signed-off-by: Bill Erickson <berick@esilibrary.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>