AMQP-287 Slow Startup is No Longer Fatal

Previously, if the consumer failed to start within 60 seconds
it was considered fatal. If the server is down and the network
is configured to take more than 60 seconds to report dropped
SYN (socket open) packets, the context would fail to initialize.

This is not consistent with, say, when the server is up but the
broker is down. In that case, the connection failure is detected
immediately, and the consumer starts attempting to reconnect - it
is NOT considered a fatal exception.

This change removes the fatal exception thrown when the consumer
fails to start in the 60 seconds (while still waiting for up to
60 seconds to see if a real fatal exception occurred).

Note that a real fatal exception (such as failure to declare the
queue(s) passively) will still cause the context to fail to initialize,
if it occurs within 60 seconds of the consumer starting.