Add missing parameter in prepare_service for api

Although the bug #1526888 (prepare_service() - duplicate function) got merged
https://review.openstack.org/#/c/258007/ we didn't see that the file in
(watcher/cmd/api.py) api didn't have sys.argv parameter.

Change-Id: I458b4ff169684131a20ef6ac090b1c918f08d427
Closes-Bug: 1526888

watcher/cmd/api.py

@@ -19,6 +19,7 @@
 
 import logging as std_logging
 import os
+import sys
 from wsgiref import simple_server
 
 from oslo_config import cfg
@@ -34,7 +35,7 @@ CONF = cfg.CONF
 
 
 def main():
-    service.prepare_service()
+    service.prepare_service(sys.argv)
 
     app = api_app.setup_app()