Occasional frame loss when shutting down connection supervision tree.

[kjnilsson]

This was found as part of the rabbitmq_shovel amqp10_dynamic test suite.

There is a chance that frames sent from the rabbit_amqp1_0_reader to the rabbit_amqp1_0_session process do not have time to be processed by the session before the connection shuts down in response to an v1_0.close{} frame being received. The chance is higher when the connection is closed straight after sending a large batch of messages such as when a shovel auto deletes itself.

The issue is hard to reproduce on many systems.