Fix NoneType object bug in Metis (#814)

* add different tuner config files for config_test

* change MetisTuner config test due to no lightgbm python module in integration test

* install smac package in azure-pipelines

* SMAC need swig to be installed

* Try to install swig from source code

* remove SMAC test because the dependency can not be installed

* use sudo to install the swig

* sleep 10s to make sure the port has been released

* remove tuner test for networkmorphism because it uses more than 30s to release the tcp port

* word "down" to "done"

* add config test for Curvefitting assessor

* change file name

* Fix data type not match bug

* Optimize MetisTunner

* pretty the code

* Follow the review comment

* add exploration probability

* Avoid None type object generating

src/sdk/pynni/nni/metis_tuner/metis_tuner.py

@@ -95,7 +95,7 @@ class MetisTuner(Tuner):
         self.samples_x = []
         self.samples_y = []
         self.samples_y_aggregation = []
-        self.history_parameters = set()
+        self.history_parameters = []
         self.space = None
         self.no_resampling = no_resampling
         self.no_candidates = no_candidates
@@ -412,8 +412,12 @@ class MetisTuner(Tuner):
         outputs = self._pack_output(lm_current['hyperparameter'])
         ap = random.uniform(0, 1)
         if outputs in self.history_parameters or ap<=self.exploration_probability:
+            if next_candidate is not None:
                 outputs = self._pack_output(next_candidate['hyperparameter'])
-        self.history_parameters.add(outputs)
+            else:
+                random_parameter = _rand_init(self.x_bounds, self.x_types, 1)[0]
+                outputs = self._pack_output(random_parameter)
+        self.history_parameters.append(outputs)
         return outputs