Message Order Not Preserved

[pascaldekloe]

Messages must be received in the same order as initially send.

integration-test-1       | === NAME  TestRoundtrip/volantmq/at-least-once
integration-test-1       |     integration_test.go:76: got message # 1, want # 0
integration-test-1       |     integration_test.go:76: got message # 2, want # 1
integration-test-1       |     integration_test.go:76: got message # 3, want # 2
integration-test-1       |     integration_test.go:76: got message # 4, want # 3
integration-test-1       |     integration_test.go:76: got message # 5, want # 4
integration-test-1       |     integration_test.go:76: got message # 6, want # 5
integration-test-1       |     integration_test.go:76: got message # 7, want # 6
integration-test-1       |     integration_test.go:76: got message # 8, want # 7
integration-test-1       |     integration_test.go:76: got message # 0, want # 8
integration-test-1       | === NAME  TestRoundtrip/volantmq/exactly-once
integration-test-1       |     integration_test.go:76: got message # 5, want # 4
integration-test-1       |     integration_test.go:76: got message # 6, want # 5
integration-test-1       |     integration_test.go:76: got message # 7, want # 6
integration-test-1       |     integration_test.go:76: got message # 8, want # 7
integration-test-1       |     integration_test.go:76: got message # 4, want # 8