daemonized start: exit children on failure, don't return

daemonized start: exit children on failure, don't return

When starting a daemonized container, only the original parent
thread should return to the caller.  The first forked child
immediately exits after forking, but the grandparent child
was in some places returning on error - causing a second instance
of the calling function.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Tycho Andersen <tycho.andersen@canonical.com>