Adds tcp_keepalive and tcp_keepidle config options

Currently the wsgi server will not close connections once requests
complete and will not enable keepalive on it's wsgi sockets. This can
be a problem for those who need to align the server keepalive with
load balancer timeouts without modifying system keepalive settings.

To remedy this we add new config options tcp_keepalive and
tcp_keepidle which are disabled by default to remain backwards
compatible.

DocImpact: "new config options for wsgi tcp_keepalive & tcp_keepidle"
Closes-bug: bug 1260406
Co-authored-by: Hirofumi Ichihara <ichihara.hirofumi@lab.ntt.co.jp>
Change-Id: Ic53402c57e1ebe44cde4c18e5e15200dcbbcb04b
Remove default_notification_level from conf

This config option is used when you use the notify_wrapper wrapper
function from openstack.common. As we don't use the wrapper we don't
ever require the config option so we shouldn't show it to users.

blueprint oslo-messaging

Change-Id: I95280af37a84c71131fb2fc92c9302b8926c95bd
Merge "Adds tcp_keepalive and tcp_keepidle config options"
Merge "Remove default_notification_level from conf"