issues #16, #20: fix cache supervisor rabbit_boot_step

The cache supervisor boot step was starting the process directly via
the `start_link` function. This is error prone as we are not sure
about the life-cycle of the bootstrap process.

It appeared to work during a proper bootstrap of the broker but was
faulty when enabling the plugin on a running one.

This patch starts the cache supervisor as a child of the main rabbit
supervisor process correctly ensuring its management.

Signed-off-by: Matteo Cafasso <[email protected]>

Author: noxdafox

lib/supervisor.ex

@@ -20,18 +20,15 @@ defmodule RabbitMQ.MessageDeduplicationPlugin.Supervisor do
   @rabbit_boot_step {
     __MODULE__,
     [description: "message deduplication plugin cache supervisor",
-     mfa: {__MODULE__, :start_link, []},
+     mfa: {:rabbit_sup, :start_child, [__MODULE__]},
      requires: :database,
      enables: :external_infrastructure]}
 
   @doc """
   Start the Supervisor process.
   """
   def start_link() do
-    case DynamicSupervisor.start_link(__MODULE__, [], name: __MODULE__) do
-      {:ok, _pid} -> :ok
-      _ -> :error
-    end
+    DynamicSupervisor.start_link(__MODULE__, [], name: __MODULE__)
   end
 
   @doc """