The headers option in apache::vhost is required in some case, for
example when adding the X-XSS-Protection header. This change allows
customizing the option for the api vhost.
This change also adds support for request_headers so that both request
headers and response headers can customized.
Change-Id: I8fd01cee29c1d906e3f427a15b5f0b23a8f29049