Display all server log when --lines option is None

Without --lines option, `console log show xxx`
cmd will break.

Change-Id: I4027aacac245e6916c1808fd9f878fb708c8a5f0
Closes-Bug: #1316870

Author: Yejia Xu

openstackclient/compute/v2/console.py

@@ -55,9 +55,13 @@ def take_action(self, parsed_args):
             compute_client.servers,
             parsed_args.server,
         )
-        # NOTE(dtroyer): get_console_output() appears to shortchange the
-        #                output by one line
-        data = server.get_console_output(length=parsed_args.lines + 1)
+        length = parsed_args.lines
+        if length:
+            # NOTE(dtroyer): get_console_output() appears to shortchange the
+            #                output by one line
+            length += 1
+
+        data = server.get_console_output(length=length)
         sys.stdout.write(data)
         return