Downgrade warning to a trace in autoload-db.cpp

Downgrade warning to a trace in autoload-db.cpp

Summary:
While running scripts with `phps`, I saw messages in my console:

```
[jhemphill@devbig351.ftw3 ~/www] phps ScriptEmptyController
WARNING: Logging before InitGoogleLogging() is written to STDERR
W0505 17:38:29.269960 2895615 RetryingSender.cpp:430] Failed to make rpc. Sender name: pr. Reason: folly::FutureNoTimekeeper: No timekeeper available.
Could not chown(/dev/shm/facts/facts_noschema.sql3-shm, -1, 2001): errno=1
Could not chmod(/dev/shm/facts/facts_noschema.sql3-shm, 436): errno=1
Could not chown(/dev/shm/facts/facts_noschema.sql3-wal, -1, 2001): errno=1
Could not chmod(/dev/shm/facts/facts_noschema.sql3-wal, 436): errno=1
```

I'm about to brag about how I fixed the first two warning messages, but that will ring a bit hollow if I'm about to add four new warning messages on every script invocation {emoji:1f613}

Reviewed By: ricklavoie

Differential Revision: D28248060

fbshipit-source-id: 37113ae5f04b3942c3e16a79c3d404627a4dfe94