Setup environment in release.sh

- These don't propagate upwards from invoking continuous.sh, so be sure
to define them.

Change-Id: I86a9ee7a44bbf2b497135d2bedeaafd34473da2b
diff --git a/kokoro/release.sh b/kokoro/release.sh
index 6c09740..4e8daa9 100644
--- a/kokoro/release.sh
+++ b/kokoro/release.sh
@@ -7,6 +7,16 @@
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 bash ${SCRIPT_DIR}/continuous.sh
 
+pushd git/continuous-build
+source build/setup.sh
+popd
+
+export TARBALL_FETCH_ROOT_DIRECTORY=${KOKORO_GFILE_DIR}
+export PREBUILT_MODULES_ROOT=${KOKORO_GFILE_DIR}
+export PREBUILT_DOCKER_ROOT=${KOKORO_GFILE_DIR}
+export DEBOOTSTRAP_TARBALL_REVISION=.
+export ROOTFS_REVISION=.
+
 m docker-make-repo
 
 m sign-repo