Adds region to examples [(#1378)](GoogleCloudPlatform/python-docs-samples#1378)

Author: gguuss

samples/api-client/manager/README.rst

@@ -88,11 +88,9 @@ To run this sample:
 
         python manager.py \
           --project_id=my-project-id \
-          --pubsub_topic=projects/my-project-id/topics/my-topic-id \
-          --ec_public_key_file=../ec_public.pem \
-          --rsa_certificate_file=../rsa_cert.pem \
-          --service_account_json=$HOME/service_account.json
-          list
+          --cloud_region=us-central1 \
+          --service_account_json=$HOME/service_account.json \
+          list-registries
 
     positional arguments:
       {create-es256,create-registry,create-rsa256,create-topic,create-unauth,delete-device,delete-registry,get,get-config-versions,get-iam-permissions,get-registry,get-state,list,list-registries,patch-es256,patch-rs256,set-config,set-iam-permissions}

samples/api-client/manager/manager.py

@@ -23,11 +23,9 @@
 
     python manager.py \\
       --project_id=my-project-id \\
-      --pubsub_topic=projects/my-project-id/topics/my-topic-id \\
-      --ec_public_key_file=../ec_public.pem \\
-      --rsa_certificate_file=../rsa_cert.pem \\
-      --service_account_json=$HOME/service_account.json
-      list
+      --cloud_region=us-central1 \\
+      --service_account_json=$HOME/service_account.json \\
+      list-registries
 """
 
 import argparse
@@ -501,16 +499,13 @@ def parse_command_line_args():
             description=__doc__,
             formatter_class=argparse.RawDescriptionHelpFormatter)
 
-    # Required arguments
+    # Optional arguments
+    parser.add_argument(
+            '--cloud_region', default='us-central1', help='GCP cloud region')
     parser.add_argument(
             '--pubsub_topic',
-            required=True,
             help=('Google Cloud Pub/Sub topic. '
                   'Format is projects/project_id/topics/topic-id'))
-
-    # Optional arguments
-    parser.add_argument(
-            '--cloud_region', default='us-central1', help='GCP cloud region')
     parser.add_argument(
             '--config',
             default=None,
@@ -597,11 +592,15 @@ def run_create(args):
                 args.cloud_region, args.registry_id, args.device_id)
 
     elif args.command == 'create-registry':
+        if (args.pubsub_topic is None):
+            sys.exit('Error: specify --pubsub_topic')
         open_registry(
                 args.service_account_json, args.project_id,
                 args.cloud_region, args.pubsub_topic, args.registry_id)
 
     elif args.command == 'create-topic':
+        if (args.pubsub_topic is None):
+            sys.exit('Error: specify --pubsub_topic')
         create_iot_topic(args.project_id, args.pubsub_topic)