Rationalize handling of quiet_level in config.c

Formerly, we would use quiet_level as an excuse to rewrite the log
configuration, adding a default log line if none existed, and if
RunAsDaemon was not set, and if we were not being invoked via
setconf (!).

This is against our best practices for several reasons:
  * We should not be changing configured options except when the
    user tells us to do so.
  * We should especially not be changing options in the options_validate
    function.
  * Distinguishing whether we are being called from setconf adds a
    risky special-case.

Instead, this patch take a simpler approach: it changes the
interpretation of having no logging lines set to mean: If there is a
stdout, add a default log based on quiet_level.

Solves ticket 31999.