Use Python to compute release notes version
Use Python to compute release notes version

Leave the version fields blank, since the release notes document
applies to all versions.
That will avoid manual changes in the future like we did until now.

Change-Id: Ie3ab0ab77d81c93ad684bb7c6ea79423d88d940a

CiscoSystems/puppet-neutron,CiscoSystems/puppet-neutron,fuel-infra/puppet-neutron,fuel-infra/puppet-neutron,openstack/puppet-neutron,fuel-infra/puppet-neutron,CiscoSystems/puppet-neutron,openstack/puppet-neutron