Set hash seed to 0 in gendocs environment
Set hash seed to 0 in gendocs environment

This was done in the venv environment to fix docs builds in the gate,
but they still fail randonly locally when using the tox environment to
build them. This change ensures the gendocs environment works for
generating documentation locally.

Change-Id: I41e4af9edaaa76b837a6c92a296b5738c85b632b

ionutbalutoiu/ironic,supermari0/ironic,SauloAislan/ironic,NaohiroTamura/ironic,redhat-openstack/ironic,dims/ironic,ionutbalutoiu/ironic,SauloAislan/ironic,naterh/ironic,Tan0/ironic,bacaldwell/ironic,pshchelo/ironic,pshchelo/ironic,openstack/ironic,naototty/vagrant-lxc-ironic,rdo-management/ironic,dims/ironic,openstack/ironic,devananda/ironic,hpproliant/ironic,NaohiroTamura/ironic,bacaldwell/ironic,naototty/vagrant-lxc-ironic