Add default IP version and fix help messages for "ip availability list"

There was not a default IP version in "ip availability list"
command, if we used this command without "--ip-version" option,
the output was different from the outputs with the option
"--ip-version 4" and "--ip-version 6" and it is not right.
This patch add default IP version (default is 4) in ``ip
availability list`` command and make this command work properly
without ``--ip-version`` option. And also fix the help message.

Change-Id: Idc08ab6eaf05946eb2ab59bfb3d4497a383d987d
Closes-Bug: #1592761

Author: Huanxuan Ao

doc/source/command-objects/ip-availability.rst

@@ -25,7 +25,7 @@ number of allocated IP addresses from that pool.
 .. option:: --ip-version {4,6}
 
     List IP availability of given IP version networks
-    (Default is 4)
+    (default is 4)
 
 .. option:: --project <project>
 

openstackclient/network/v2/ip_availability.py

@@ -41,15 +41,17 @@ def get_parser(self, prog_name):
         parser.add_argument(
             '--ip-version',
             type=int,
+            default=4,
             choices=[4, 6],
             metavar='<ip-version>',
             dest='ip_version',
-            help=_("List IP availability of given IP version networks"),
+            help=_("List IP availability of given IP version "
+                   "networks (default is 4)"),
         )
         parser.add_argument(
             '--project',
             metavar='<project>',
-            help=_("List IP availability of given project"),
+            help=_("List IP availability of given project (name or ID)"),
         )
         identity_common.add_project_domain_option_to_parser(parser)
         return parser

openstackclient/tests/network/v2/test_ip_availability.py

@@ -82,8 +82,10 @@ def test_list_no_options(self):
         parsed_args = self.check_parser(self.cmd, arglist, verifylist)
 
         columns, data = self.cmd.take_action(parsed_args)
+        filters = {'ip_version': 4}
 
-        self.network.network_ip_availabilities.assert_called_once_with()
+        self.network.network_ip_availabilities.assert_called_once_with(
+            **filters)
         self.assertEqual(self.columns, columns)
         self.assertEqual(self.data, list(data))
 
@@ -116,7 +118,8 @@ def test_list_project(self):
         parsed_args = self.check_parser(self.cmd, arglist, verifylist)
 
         columns, data = self.cmd.take_action(parsed_args)
-        filters = {'tenant_id': identity_fakes.project_id}
+        filters = {'tenant_id': identity_fakes.project_id,
+                   'ip_version': 4}
 
         self.network.network_ip_availabilities.assert_called_once_with(
             **filters)

releasenotes/notes/bug-1592761-f45998453d6801f7.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - Add default IP version in ``ip availability list`` command and make
+    this command work properly without ``--ip-version`` option.
+    [Bug `1592761 <https://bugs.launchpad.net/bugs/1592761>`_]