test: fix flaky persistent triggers test

The replication test of persistent triggers was waiting only for
the persistent triggers to arrive on replica, so the replica tried
to write to the space which was not created there yet. Let's wait
for all changes to arrive to make the test stable.

Closes #9967

NO_CHANGELOG=test
NO_DOC=test

test/box-luatest/gh_8663_persistent_triggers_test.lua

@@ -283,21 +283,16 @@ g.test_replicated_non_idempotent_trigger = function(g)
         box.space.weights:replace{'elephant', 4000}
         box.space.weights:replace{'crocodile', 600}
     end)
+    -- Wait for the trigger and the space to arrive on the second server
+    g.server2:wait_for_vclock_of(g.server1)
     g.server2:exec(function()
-        -- Wait for a trigger to arrive
-        while box.func['example.replicated_trigger'] == nil do
-            require('fiber').sleep(0)
-        end
         box.space.weights:replace{'cat', 6}
         box.space.weights:replace{'dog', 10}
     end)
 
-    -- Check result
+    -- Wait for the writes to arrive on the first server
+    g.server1:wait_for_vclock_of(g.server2)
     local check_case = function(expected_result)
-        -- Wait for both servers
-        while box.space.weights:count() ~= 4 do
-            require('fiber').sleep(0)
-        end
         t.assert_equals(box.space.weights:select(nil, {fullscan=true}),
             expected_result)
     end