requirements: Be more specific about urllib3 pin origin
requirements: Be more specific about urllib3 pin origin

In order to make it much clearer where the pin comes from,
we provide a link to the source.

Change-Id: I018c47422eb01ac0b1e9761cf29050adc782b00e

redhat-openstack/infrared,redhat-openstack/infrared,redhat-openstack/infrared