lxc.init: correctly exit with the app's error code

lxc.init: correctly exit with the app's error code

Based on the comments in the code (and the have_status flag), the intent
here (and IMO, the desired behavior) should be for init.lxc to propagate
the actual exit code from the real application process up through.
Otherwise, it is swallowed and nobody can access it.

The bug being fixed here is that ret held the correct exit code, but when
it went around the loop again (to wait for other children) ret is
clobbered. Let's save the desired exit status somewhere else, so it can't
get clobbered, and we propagate things correctly.

Signed-off-by: Tycho Andersen <tycho@tycho.ws>