Switch to POLL_TEMP_URL for config transport

Switch to POLL_TEMP_URL for config transport

This will allow the following:
- reduced load on heat for large overclouds
- a shorter os-collect-config poll interval without increasing load on
  the undercloud
- the ability to add config deployments outside the stack, allowing
  workflow tools like mistral, ansible or tripleoclient to directly
  deploy custom scripts and config to overcloud nodes

Change-Id: If028c9d7764210363135c3e7cc16ae1fb897a77c
Depends-On: I9c475f0c489c67db5895924050186228403f2773