AutoML Tables: Passing client_info produces a a TypeError

[vimota]

Environment details

1. Linux.
2. python 3.7
3. Latest google-cloud-python master branch

Steps to reproduce

1. Initializing the automl tables client with a client_info parameter throws a TypeError due to it being passed twice to the underlying clients.

Code example

client = automl_v1beta1.TablesClient(client_info=client_info)

A more thorough example in this PR (where we have to make an exception of setting the ClientInfo due to the error): https://github.com/Kaggle/docker-python/pull/671/files.

Stack trace

TypeError: type object got multiple values for keyword argument 'client_info'.

It should be a pretty easy fix, putting together the PR now :)