Use debian9 as base image instead of base. (#129)
Use debian9 as base image instead of base. (#129)

* Use debian9 as base image instead of base.

gcr.io/google-appengine/base uses debian8 as its base, which is EOL. This is causing this dockerfile to fail to build on apt-get. This debian9 image should contain everything needed to be a drop in replacement for base.

* install gnupg2

GoogleCloudPlatform/appengine-sidecars-docker,GoogleCloudPlatform/appengine-sidecars-docker