Comment 4 for bug 1227912

Hi Ravi, I also got this issue when I test my codes under devstack, and this is the comment about this issue:
https://review.openstack.org/#/c/36372/6..7/etc/nova/nova.conf.sample
The original method to fix this issue is adding a config item for storing the socket file on the host, but Daniel doesn't like this, and I think the better way to notify the user about this trap is adding some doc to the release notes.