Fix --enable options on commands

The --enable option on commands is ignored when the arguments are parsed.
This is related to the --enable-beta-commands option. Renaming the option
to --os-beta-command fixes the problem.

There's no need to handle backwards compatibility for the option name
change because there hasn't been an OSC release yet with beta commands.

Change-Id: I0327ba8a2058858a83e9a42e231470ed733cc834
Closes-Bug: #1588384

openstackclient/shell.py

@@ -251,7 +251,7 @@ class OpenStackShell(app.App):
             help="Print API call timing info",
         )
         parser.add_argument(
-            '--enable-beta-commands',
+            '--os-beta-command',
             action='store_true',
             help="Enable beta commands which are subject to change",
         )