Add metavar for --fixed-ip

This patch adds a metavar for the --fixed-ip option so that it's
more clear that the user needs to pass in ip_address=IP_ADDR.

Fixes bug 1188889

Change-Id: I66efd444a2df52603f124637072f194497e241e2

quantumclient/quantum/v2_0/port.py

@@ -109,7 +109,7 @@ class CreatePort(CreateCommand):
             '--device_id',
             help=argparse.SUPPRESS)
         parser.add_argument(
-            '--fixed-ip',
+            '--fixed-ip', metavar='ip_address=IP_ADDR',
             action='append',
             help='desired IP for this port: '
             'subnet_id=<name_or_id>,ip_address=<ip>, '