Move client utils into separate file

Summary:
## Overview

This diff:
* Moves all client methods that not rely on class state and do not use DB to their own client_utils file
* Moves the client test file to the /test directory

## Motivation

* Reduces size of metro_client.py file.  Customers will look at our client.py file for API methods.  Ideally we keep this as simple as possible

* Testing - We can use the same methods in our integration tests that we do in normal upload (followup diff).  We can also more easily write unit tests for the util methods

Differential Revision: D56492839

fbshipit-source-id: 4a2a1d39db6446ca6ab305a877b0c69d5442fd03

testslide/__init__.py

@@ -22,7 +22,6 @@
 from contextlib import contextmanager
 from functools import partial
 from typing import (
-    TYPE_CHECKING,
     Any,
     Callable,
     Dict,
@@ -32,6 +31,7 @@
     TextIO,
     Tuple,
     Type,
+    TYPE_CHECKING,
     Union,
 )