Switch release version backend to git
Switch release version backend to git

[#153644290](https://www.pivotaltracker.com/story/show/153644290)

Signed-off-by: Florian Nachtigall <da0e822b67ef154a118f514785d782d9f0817746@sap.com>

cloudfoundry-incubator/bosh-openstack-cpi-release,cloudfoundry-incubator/bosh-openstack-cpi-release,cloudfoundry-incubator/bosh-openstack-cpi-release