otptoken-add-yubikey: When --digits not provided use default value

Since Thin client was introduced default values for options are not populated
in client side plugins. When option has default value and is needed in client
plugin it must be handled by explicitly.

https://pagure.io/freeipa/issue/6900

Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>

ipaclient/plugins/otptoken_yubikey.py

@@ -147,7 +147,10 @@ class otptoken_add_yubikey(Command):
 
         # Write the config.
         cfg = yk.init_config()
-        cfg.mode_oath_hotp(key, kwargs['ipatokenotpdigits'])
+        cfg.mode_oath_hotp(key, kwargs.get(
+            'ipatokenotpdigits',
+            self.get_default_of('ipatokenotpdigits')
+        ))
         cfg.extended_flag('SERIAL_API_VISIBLE', True)
         yk.write_config(cfg, slot=kwargs['slot'])