Deprecate 'novaclient.client.get_client_class'
Deprecate 'novaclient.client.get_client_class'

This method is redundant and blocks versioned client classes to change
interface. `novaclient.client.Client` should be used instead.

Releated-Bug: #1493576
Change-Id: I73cea2c6062419d75646e9239c6194f4d1ffd2b1

mat128/python-novaclient,mat128/python-novaclient,takeshineshiro/python-novaclient,takeshineshiro/python-novaclient