Pin voluptuous <0.7.
Pin voluptuous <0.7.

* tools/pip-requires: A new voluptuous (0.7.0) was released today,
introducing backward-incompatible changes to schema objects and
breaking zuul's layout validation. This is a brown bag fix to keep
zuul functional until voluptuous 0.7 support is implemented.

Change-Id: I5818d3cd529e8682877b368edbc10280a5c167df
Reviewed-on: https://review.openstack.org/24454
Reviewed-by: Anita Kuno <a4cb37fdbed276720704fae24269d19ff379fea4@lavabit.com>
Reviewed-by: Monty Taylor <37c07a49ee3d5191376d758eb1d8298b34456b8e@inaugust.com>
Approved: James E. Blair <e81a02a9d6405977f63a769d9f6ec8ed9d924325@inaugust.com>
Reviewed-by: James E. Blair <e81a02a9d6405977f63a769d9f6ec8ed9d924325@inaugust.com>
Tested-by: Jenkins

wikimedia/integration-zuul,gooddata/zuul,wikimedia/integration-zuul,devdattakulkarni/zuul_messaging,gooddata/zuul,devdattakulkarni/zuul_messaging,gooddata/zuul,devdattakulkarni/zuul_messaging,wikimedia/integration-zuul,gooddata/zuul,wikimedia/integration-zuul,gooddata/zuul