Properly log errors when setting up daemon FDs

While writing the pipe-based reporting and trying various ways to
break the startup, I fought for a while trying to understand why error
reporting was _different_ when running the daemon as a user (with no
rights). It turns out that setupDaemonFDs wants to open the log file
in append mode way before, so we are not protected by the 'prepare'
phase.

This patch explicitly runs the 'setupDaemonFDs' function under the
same handler as the prepare phase, with the only change that here we
instruct handlePrepErr to not log the message via log*, since logging
is not yet set up.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>