Don't throw valueerror on bootstrap

When keystone-manage bootstrap is ran without providing a value
to set as the admin password, keystone-manage will throw an
unhandled ValueError while displaying the proper warning
message.

This change removes the ValueError and simply has the CLI
exit out when this condition is met.

Closes-Bug: #1804700

Change-Id: I4e7d5eeb2e48ff354b44196bd11d62d51a73357b

keystone/cmd/cli.py

@@ -152,9 +152,9 @@ class BootStrap(BaseApp):
         self.endpoints = None
 
         if self.password is None:
-            print(_('Either --bootstrap-password argument or '
+            print(_('ERROR: Either --bootstrap-password argument or '
                     'OS_BOOTSTRAP_PASSWORD must be set.'))
-            raise ValueError
+            sys.exit(1)
 
         self.bootstrapper.admin_password = self.password
         self.bootstrapper.admin_username = self.username