tempest: add kibana_version to the identity senction of tempest.conf

[sjamgade]

kibana_version conf is needed by monasca_log_api_tempest testcases as this key-value pair is added headers of requests to kibana https://opendev.org/openstack/monasca-log-api/src/tag/newton-eol/monasca_log_api_tempest/config.py#L40

sample failure: https://ci.suse.de/job/openstack-mkcloud/8437/consoleText

[JanZerebecki]

Looks good, but needs rebase.