py3: vault: data must be bytes

Use bytes for vault data

https://pagure.io/freeipa/issue/4985

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

ipaclient/plugins/vault.py

@@ -827,7 +827,7 @@ class vault_archive(ModVaultData):
             data = validated_read('in', input_file, mode='rb')
 
         else:
-            data = ''
+            data = b''
 
         if self.api.env.in_server:
             backend = self.api.Backend.ldap2