CSI test: Fix race when slave becomes active again

Make sure the server processed the slave's active request after the
previous test stanzas were received by the slave and before the final
Chat State notification is sent by the master.

test/ejabberd_SUITE.erl

@@ -1575,16 +1575,17 @@ client_state_master(Config) ->
     Message = #message{to = Peer, thread = <<"1">>,
 		       sub_els = [#chatstate{type = active}]},
     wait_for_slave(Config),
-    %% Should be queued (but see below):
-    send(Config, Presence),
-    %% Should be sent immediately, together with the previous presence:
-    send(Config, Message#message{body = [#text{data = <<"body">>}]}),
     %% Should be dropped:
     send(Config, Message),
     %% Should be queued (but see below):
-    send(Config, Presence),
-    %% Should replace the previous presence in the queue:
     send(Config, Presence#presence{type = unavailable}),
+    %% Should replace the previous presence in the queue:
+    send(Config, Presence),
+    %% Should be sent immediately, together with the previous presence:
+    send(Config, Message#message{body = [#text{data = <<"body">>}]}),
+    %% Should be queued:
+    send(Config, Presence#presence{type = unavailable}),
+    %% Wait for the slave to become active.
     wait_for_slave(Config),
     %% Should be sent immediately, as the client is active again.
     send(Config, Message),
@@ -1601,11 +1602,12 @@ client_state_slave(Config) ->
     ?recv1(#presence{from = Peer, sub_els = [#vcard_xupdate{}|_]}),
     ?recv1(#message{from = Peer, thread = <<"1">>, sub_els = [#chatstate{type = active}],
 	     body = [#text{data = <<"body">>}]}),
-    wait_for_master(Config),
     send(Config, #csi{type = active}),
-    ?recv2(#presence{from = Peer, type = unavailable,
-		     sub_els = [#delay{}, #legacy_delay{}]},
-	   #message{from = Peer, thread = <<"1">>,
+    %% The server now flushes the queue, so we receive the following presence.
+    ?recv1(#presence{from = Peer, type = unavailable,
+		     sub_els = [#delay{}, #legacy_delay{}]}),
+    wait_for_master(Config),
+    ?recv1(#message{from = Peer, thread = <<"1">>,
 		    sub_els = [#chatstate{type = active}]}),
     disconnect(Config).