Use a relative URL for status.json.

So that app.js can be less specific about where it's running.

Change-Id: I2a84a659b43027b7eb59ba707396517d8ba635d3
Reviewed-on: https://review.openstack.org/29286
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Approved: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins