Reset VM memory watermark during setup and tear down

Otherwise connections in other tests may end up being blocked,
which in turn means functions that close network connections time
out.

deps/rabbitmq_cli/test/set_vm_memory_high_watermark_command_test.exs

@@ -24,8 +24,11 @@ defmodule SetVmMemoryHighWatermarkCommandTest do
   setup_all do
     :net_kernel.start([:rabbitmqctl, :shortnames])
     :net_kernel.connect_node(get_rabbit_hostname)
+    :vm_memory_monitor.set_vm_memory_high_watermark(0.4)
 
     on_exit([], fn ->
+      :vm_memory_monitor.set_vm_memory_high_watermark(0.4)
+
       :erlang.disconnect_node(get_rabbit_hostname)
       :net_kernel.stop()
     end)