Description of problem:
When Director deployed with DVR, tempest configuration (deployer input) should include the following configuration:
neutron_plugin_options.l3_agent_mode='dvr_snat'
In order for relevant DVR tests in neutron tempest plugin to run.
I believe it doesn't make sense for CI systems to manually insert it.
Version-Release number of selected component (if applicable): any release that supports DVR
While we could add a single additional line for this configuration setting, the bug report suggests the need for a generalized mechanism for mapping the values of heat environment variables to tempest-deployer-input.conf.