darwin-d3 & ldb crash horribly if rabbitmq is not available

[peter-mount]

This brought departureboards down earlier as rabbitmq has died:

go/src/bin/darwind3/main.go:10 +0x2d
2018/04/16 07:25:20 /darwind3 d7b3ea2 linux(amd64) linux(amd64)
2018/04/16 07:25:20 Connecting to amqp
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x687e90]
goroutine 1 [running]:
github.com/streadway/amqp.(*Connection).allocateChannel(0x0, 0x0, 0x0, 0x0)
/go/src/github.com/streadway/amqp/connection.go:589 +0x40
github.com/streadway/amqp.(*Connection).openChannel(0x0, 0xc42004bd70, 0x674918, 0x7287a0)
/go/src/github.com/streadway/amqp/connection.go:619 +0x2f
github.com/streadway/amqp.(*Connection).Channel(0x0, 0x2, 0xc4200559f0, 0x1)
/go/src/github.com/streadway/amqp/connection.go:646 +0x2b
github.com/peter-mount/golib/rabbitmq.(*RabbitMQ).NewChannel(0xc4201140c0, 0xc42005ac60, 0x0, 0xc42004bdc0)
/go/src/github.com/peter-mount/golib/rabbitmq/rabbitmq.go:96 +0x2f
darwind3.(*DarwinD3).BindConsumer(0xc420056700, 0xc4201140c0, 0xc4200228c8, 0x7, 0xc4200228f0, 0x8, 0x0, 0x1)
/go/src/darwind3/consumer.go:13 +0x32
main.app(0xc420114000, 0x0, 0x0, 0x0)
/go/src/bin/darwind3/main.go:41 +0x270
bin.RunApplication(0x7b45f0)
/go/src/bin/main.go:50 +0x43e
main.main()
/go/src/bin/darwind3/main.go:10 +0x2d
No newer events found at the moment. Retry.