Explain the "or None" on eventlet's client_socket_timeout
Explain the "or None" on eventlet's client_socket_timeout

This certainly caught me off guard, so I added an inline comment to
explain the code based on the discussion here:

  https://review.openstack.org/#/c/177443/1/keystone/common/environment/eventlet_server.py

Change-Id: I9ca4b4382e9a3236019a7bacc9459d587a682e10

klmitch/keystone,cernops/keystone,cernops/keystone,vivekdhayaal/keystone,himanshu-setia/keystone,mahak/keystone,rajalokan/keystone,ajayaa/keystone,takeshineshiro/keystone,openstack/keystone,himanshu-setia/keystone,ilay09/keystone,mahak/keystone,idjaw/keystone,jamielennox/keystone,klmitch/keystone,maestro-hybrid-cloud/keystone,maestro-hybrid-cloud/keystone,vivekdhayaal/keystone,mahak/keystone,jamielennox/keystone,dims/keystone,dstanek/keystone,roopali8/keystone,ajayaa/keystone,vivekdhayaal/keystone,dstanek/keystone,takeshineshiro/keystone,openstack/keystone,roopali8/keystone,idjaw/keystone,dims/keystone,openstack/keystone,ilay09/keystone,ilay09/keystone,jonnary/keystone,jonnary/keystone,rajalokan/keystone,dstanek/keystone,rajalokan/keystone