qga: Don't daemonize before channel is initialized

qga: Don't daemonize before channel is initialized

If the agent is set to daemonize but for whatever reason fails to
init the channel, the error message is lost. Worse, the agent
daemonizes needlessly and returns success. For instance:

  # qemu-ga -m virtio-serial \
            -p /dev/nonexistent_device \
            -f /run/qemu-ga.pid \
            -t /run \
            -d
  # echo $?
  0

This makes it needlessly hard for init scripts to detect a
failure in qemu-ga startup. Though, they shouldn't pass '-d' in
the first place.

Let's open the channel first and only after that become a daemon.

Related bug: https://bugs.gentoo.org/810628

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Konstantin Kostiuk <kkostiuk@redhat.com>
Message-ID: <7a42b0cbda5c7e01cf76bc1b29a1210cd018fa78.1736261360.git.mprivozn@redhat.com>
Signed-off-by: Konstantin Kostiuk <kkostiuk@redhat.com>