Port test_servers to py3
Port test_servers to py3

Use base64 module from oslo.serialization to handle
base64 encoding and decoding.

Change-Id: Ib44eb337acabd68eb92ddc202c09768ae89a7eb1
Partially-Implements: blueprint goal-python35

klmitch/nova,hanlind/nova,mikalstill/nova,rajalokan/nova,openstack/nova,Juniper/nova,openstack/nova,vmturbo/nova,klmitch/nova,rajalokan/nova,phenoxim/nova,mahak/nova,rajalokan/nova,hanlind/nova,rahulunair/nova,vmturbo/nova,hanlind/nova,jianghuaw/nova,gooddata/openstack-nova,mahak/nova,Juniper/nova,Juniper/nova,Juniper/nova,klmitch/nova,jianghuaw/nova,gooddata/openstack-nova,rahulunair/nova,openstack/nova,rahulunair/nova,gooddata/openstack-nova,mahak/nova,rajalokan/nova,mikalstill/nova,vmturbo/nova,mikalstill/nova,phenoxim/nova,jianghuaw/nova,klmitch/nova,jianghuaw/nova,gooddata/openstack-nova,vmturbo/nova