Fix "device" as the optional para on volume-attach

Attach a volume to a server without device name, the client returned the
error msg: "error: too few arguments". But for server, we can attach a
volume to a server without the device name.

Change-Id: Ia2743c6e3956cae6591ecd414baf89b0dbcf532b
Closes-Bug: #1257137

novaclient/tests/v1_1/test_shell.py

@@ -1790,6 +1790,13 @@ class ShellTest(utils.TestCase):
                                {'device': '/dev/vdb',
                                 'volumeId': 'Work'}})
 
+    def test_volume_attach_without_device(self):
+        self.run_command('volume-attach sample-server Work')
+        self.assert_called('POST', '/servers/1234/os-volume_attachments',
+                           {'volumeAttachment':
+                               {'device': None,
+                                'volumeId': 'Work'}})
+
     def test_volume_update(self):
         self.run_command('volume-update sample-server Work Work')
         self.assert_called('PUT', '/servers/1234/os-volume_attachments/Work',

novaclient/v1_1/shell.py

@@ -1707,7 +1707,7 @@ def do_volume_delete(cs, args):
 @utils.arg('volume',
     metavar='<volume>',
     help='ID of the volume to attach.')
-@utils.arg('device', metavar='<device>',
+@utils.arg('device', metavar='<device>', default=None, nargs='?',
     help='Name of the device e.g. /dev/vdb. '
          'Use "auto" for autoassign (if supported)')
 def do_volume_attach(cs, args):

novaclient/v3/shell.py

@@ -1557,7 +1557,7 @@ def do_volume_delete(cs, args):
 @utils.arg('volume',
     metavar='<volume>',
     help='ID of the volume to attach.')
-@utils.arg('device', metavar='<device>',
+@utils.arg('device', metavar='<device>', default=None, nargs='?',
     help='Name of the device e.g. /dev/vdb. '
          'Use "auto" for autoassign (if supported)')
 def do_volume_attach(cs, args):