Explicitly set 'builders' option
Explicitly set 'builders' option

An upcoming release of pbr will require explicitly stating which
builders are requested, rather than defaulting to html and man. Head off
any potential impact this may cause by explicitly setting this
configuration now.

Change-Id: I6983a5a988d8a595f2ab75580147da2e920ae030

rajalokan/keystone,rajalokan/keystone,mahak/keystone,mahak/keystone,openstack/keystone,mahak/keystone,rajalokan/keystone,openstack/keystone,openstack/keystone