Some node types such as config servers and master/slave setups will return "norepl" from calls to getLastError with "w":"majority.
This means that any time a user management command is run with a "majority" write concern, the command reports failure with a "norepl" error, even though the command actually succeeded.
Ideally w: "majority" would have a well-defined meaning for all cluster and node types, but barring that we should swallow "norepl" errors in the shell helpers for user and role management so users are less likely to see these (harmless) error messages. We already do this for the addUser/createUser shell helpers, so we just need to do this for the remaining user and role management helpers.