Remove legacy code from OnStop
Remove legacy code from OnStop

This changes OnStop to assume LXC 2.0.0 or higher.

So it now relies on LXC_TARGET being set in the environment (and will
fail if it's not) and also depends on LXC interrupting container restart
on hook failures.

This allows the removal of a good chunk of code and improved logging of
what's going on with the container.

Signed-off-by: Stéphane Graber <089afc6d81f66f1168a9849e15660feae286e024@ubuntu.com>

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