Add openstack-dev/sandbox to zuulv3.o.o
Add openstack-dev/sandbox to zuulv3.o.o

We need a project where we can tag (pre-)releases, add sandbox so we
can do just that.

Change-Id: Ia9164fa0b06a2b97e04d6d7365f150ee53091a2b
Signed-off-by: Paul Belanger <e7139c8e6c4ea75cc1c287ce081b2dc0f3ab39ec@redhat.com>

openstack-infra/project-config,openstack-infra/project-config