client: ignore override errors in command overrides

This fixes API initialization errors when the remote server does not have
the overriden command.

https://fedorahosted.org/freeipa/ticket/4739

Reviewed-By: David Kupka <dkupka@redhat.com>

ipaclient/plugins/idrange.py

@@ -24,7 +24,7 @@ from ipalib import api
 register = Registry()
 
 
-@register(override=True)
+@register(override=True, no_fail=True)
 class idrange_add(MethodOverride):
     def interactive_prompt_callback(self, kw):
         """