Support starting remote GCE with multiple devices inside the VM.

Bug: 146643038
Test: acloud-dev create_cf --branch git_master --build_target
cf_x86_phone-userdebug --num-avds-per-instance 2

Change-Id: I17f57a812c7903b1e63d1634494b1df9c6e9534d
diff --git a/public/acloud_main.py b/public/acloud_main.py
index 94ffe0f..b26a01e 100644
--- a/public/acloud_main.py
+++ b/public/acloud_main.py
@@ -167,6 +167,13 @@
     create_cf_parser = subparsers.add_parser(CMD_CREATE_CUTTLEFISH)
     create_cf_parser.required = False
     create_cf_parser.set_defaults(which=CMD_CREATE_CUTTLEFISH)
+    create_cf_parser.add_argument(
+        "--num-avds-per-instance",
+        type=int,
+        dest="num_avds_per_instance",
+        required=False,
+        default=1,
+        help="Number of devices to create on a gce instance.")
     create_args.AddCommonCreateArgs(create_cf_parser)
     subparser_list.append(create_cf_parser)