Fix PEP 479 issue
Fix PEP 479 issue

PEP 479 changes the behavior of generators. This change took full
effect in python 3.7, exposing an issue in one of our tests where we
were mocking file reads but not returning None when there was no more
data to read.

Partial-Bug: #1785255
Change-Id: Ib3d730d81567ec91af304b9c7b5d0f2373de9158

pypowervm/pypowervm,powervm/pypowervm