R1:e0d6994adb1c

Use the "@" operator to silence connection retry messages if initializing the stack with database config optional

Summary:
Depends on D20780. Ref T13403. During initial setup, it's routine to run "bin/config" with a bad database config. We start the stack in "config optional" mode to anticipate this.

However, even in this mode, we may emit warnings if the connection fails in certain ways. These warnings aren't useful; suppress them with "@".

(Possibly this message should move from "phlog()" to "--trace"…