Refactor main server loop a bit, to add basic retry w/ error logging

hopefully this lets us get past a simple Postgres restart..

rattail_tempmon/client.py

@@ -92,6 +92,7 @@ class TempmonClient(Daemon):
                 try:
                     session.commit()
                 except:
+                    # TODO: pretty sure we need to add a retry for this..
                     log.exception("failed to commit changes to database")
                     raise