Make test_version_string_with_package_is_good work with pbr 0.11
Make test_version_string_with_package_is_good work with pbr 0.11

nova.version uses the version_string() API not version. Fix the test to
reflect that and make it work with pbr 0.11

Closes-Bug: #1450682
Change-Id: I4887b8000c9943c91f8add56fcc54fa18e78d683

alexandrucoman/vbox-nova-driver,alexandrucoman/vbox-nova-driver