Support glance client can get ipv6 image url correctly

This patch is for fix bug 1208784. In openstack ipv6 environment,
if the os image url is not provided, need use the provided host
to generate literal ipv6 image url.

Fixes bug 1208784

Change-Id: Icb71241a639db02d079348f086bd7bd5f0412609
Merge "Support glance client can get ipv6 image url correctly"