turn on warning-is-error for doc build
turn on warning-is-error for doc build

Change-Id: Iabf25943a2e52667c4be67df654e0b2626bbb557
Signed-off-by: Doug Hellmann <0798ebecfb7bc4dfb9d0445c2fa030eb64e1fa1c@doughellmann.com>

openstack/stevedore