Enable warnings as errors
Enable warnings as errors

Warning-is-error option is avaialble in sphinx setup command
integration since Sphinx 1.5. This is useful to prevent
future warnings.
Note that there is no sphinx error or warning in the current
code base.

Change-Id: I5bfcfb436cbe5662c0702ea3a3343cd03cdd756a

openstack/freezer-web-ui,openstack/freezer-web-ui,openstack/freezer-web-ui,openstack/freezer-web-ui