gddo-server: use App Engine remoteapi for search.

App Engine Flexible Environment does not allow access to the Search API. To
temporarily get around this limitation, we are adding support for using an
App Engine standard application as a proxy. This will support future work
getting rid of App Engine specific code from the codebase entirely.

Change-Id: Id0537f4a86d1a588601e3d97d30f2be906ab23cf
Reviewed-on: https://go-review.googlesource.com/38397
Reviewed-by: Tuo Shan <shantuo@google.com>
4 files changed