Disable caching for the v2 entry point

This is currently only used by RESTBase, which will save the response. The
requests still traverse Varnish in the meantime, which means that we'd dilute
the cache at the cost of v1 performance in the meantime.

Change-Id: I0d7c8b1bc54665240029fb6f17b5e8d1ec9e69e3