Fix issue with accessIPv4 value in nova response

In some responses from the Nova admin api, the value for accessIPv4
is blank.  This patch will try to retrieve the IPv4 address from
the addresses list in such responses.

Change-Id: Id0e64c033534221bf39fae8a670470889745e055
Merge pull request #644 from dmend/verify-resource

Fix issue with accessIPv4 value in nova response