Comment 19 for bug 1466485

I encounter a similar problem in our upgrade process. The root cause for us is that keystone is upgraded parallel with neutron, both rely on python-routes(in our environment). keystone starts while neutron uninstalls python-routes. One thing to note is that the log may not reveal the real module missing due to a bug in Python2 import mechnism: https://bugs.python.org/issue32479.