Add retry logic while initializing local keystone client

PowerVC driver will authenticate hosting openstack's keystone, and we
need to add some retry logic while creating the keystone client for the
hosting openstack. 

Closes-bug: #1334508
Change-Id: Iae5936d1fdd75494ed8ec0057d8480c9626ed591
Merge "Add retry logic while initializing local keystone client"