Remove AltManager class from client

As Change-Id: I280f2b1659c593e14ab9213a161b55bcfc08fa5c has modified
the Manager instantiation for non isolated tenant, AltManager class
is no more needed.

Tests runs for non isolated by instantiating the Manager with 'alt'
credential.

This patch removes the class AltManager from client.py

Closes-Bug: #1329065

Change-Id: I0dcf4050d8524655b017b4b5308fe3070aa2f840
Merge "Remove AltManager class from client"