Rearrange tests written only for update_on_kvstore = True (apache#13514)

* Update test_gluon_trainer.py

* Update test_gluon_trainer.py

* test

tests/python/unittest/test_gluon_trainer.py

@@ -74,12 +74,13 @@ def dict_equ(a, b):
     if trainer._update_on_kvstore:
         dict_equ(trainer._kvstore._updater.states, states)
         assert trainer._optimizer == trainer._kvstore._updater.optimizer
+        # invalid usage of update and allreduce_grads if update_on_kvstore
+        assert_raises(AssertionError, trainer.update, 1)
+        assert_raises(AssertionError, trainer.allreduce_grads)
     else:
         for updater in trainer._updaters:
             dict_equ(updater.states, states)
         assert trainer._optimizer == trainer._updaters[0].optimizer
-    assert_raises(AssertionError, trainer.update, 1)
-    assert_raises(AssertionError, trainer.allreduce_grads)
 
     x = gluon.Parameter('x', shape=(10,))
     x.initialize(ctx=[mx.cpu(0), mx.cpu(1)], init='zeros')
@@ -193,8 +194,10 @@ def check_trainer_reset_kv(kv):
         # load would reset kvstore
         mx.nd.waitall()
         params.load('test_trainer_reset_kv.params')
-        assert trainer._kvstore is None
-        assert trainer._kv_initialized is False
+        if trainer._update_on_kvstore:
+            # drop kvstore state if new parameters are loaded
+            assert trainer._kvstore is None
+            assert trainer._kv_initialized is False
         with mx.autograd.record():
             for w in x.list_data():
                 y = w + 1