Automatically generate container names
spawn/1,2: return a container or throw exception

Instead of returning an error tuple, crash if spawn fails.
Destroy the container upon exit

By default, remove resources associated with the container. The
behaviour can be overridden by using:

    erlxc:spawn(<<>>, [{destroy,false}]).
dialyzer: verify examples
example: tcpvm

Connect to a TCP port and spawn an Ubuntu 12.04 container:

 tcpvm:start([{config, [{"lxc.network.link", "br0"}]}]).
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