It seems there is not an /etc/lsb-release (or /etc/redhat-release) for an OpenStack node. However, you can get the installed version in other ways. From a compute node, run the following commands:
$ nova-manage shell python Python 2.7.3 (default, Sep 26 2013, 20:03:06) [GCC 4.6.3] on linux2 Type "help", "copyright", "credits" or "license" for more information. (InteractiveConsole) >>> from nova import version >>> version.version_string() '2013.2' >>>
Source: http://fosshelp.blogspot.com/2011/09/how-to-find-openstack-nova-version.html