change lxc-autostart shutdown to behave like lxc-stop

change lxc-autostart shutdown to behave like lxc-stop

It is desirable to have a mode where a soft shutdown is requested,
but then do a hard shutdown if after some time period the container
has not shut down. This the default behaviour of lxc-stop, but is
not currently possible with lxc-autostart. This change makes this
the default behaviour when shutdown is specified to lxc-autostart.
This will be very useful for init scripts.

An indefinte wait for soft shutdown (though I'm not sure how that
would be useful) is still possible by passing a timeout of 0.

Change default timeout value to 60 seconds to match lxc-stop

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>