Change get_xxx_id's return type to meet API doc (#1780)

src/sdk/pynni/nni/platform/local.py

@@ -101,4 +101,4 @@ def get_trial_id():
     return trial_env_vars.NNI_TRIAL_JOB_ID
 
 def get_sequence_id():
-    return trial_env_vars.NNI_TRIAL_SEQ_ID
+    return int(trial_env_vars.NNI_TRIAL_SEQ_ID)

src/sdk/pynni/nni/platform/standalone.py

@@ -44,13 +44,13 @@ def get_next_parameter():
     }
 
 def get_experiment_id():
-    pass
+    return 'STANDALONE'
 
 def get_trial_id():
-    pass
+    return 'STANDALONE'
 
 def get_sequence_id():
-    pass
+    return 0
 
 def send_metric(string):
     metric = json_tricks.loads(string)