text-based mount.nfs: Add text-based error reporting function
The mount_errors() function prints an error based on what just happened in
the user-space RPC library. This is meaningless for text-based mounts,
since they don't use the RPC library for most things.
Add a new error printing function that the text-based logic can use to
report an error.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Neil Brown <neilb@suse.de>