daemon.py: move startup log message before prep_fn

Before this, the output in the rapi daemon log was:
2011-04-04 03:09:51,026: ganeti-rapi pid=17447 INFO Reading users file
at /var/lib/ganeti/rapi/users
2011-04-04 03:09:51,027: ganeti-rapi pid=17447 INFO ganeti-rapi daemon
startup

Which is confusing, as it might look like the read of the users file
is part of the previous run. This is because we log the 'daemon
startup' message after the prepare_fn, which can log things on its
own.

The patch simply moves the 'daemon startup' message just before
prepare_fn call.

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