Upload the nightly release to a "nightly/latest" bucket for easy download.

We also upload to a path with the current date, so that previous builds are
archived. Since these builds only include the date (and not time) their links
are somewhat discoverable as well.

PiperOrigin-RevId: 196147475
Change-Id: I54792d7a4ba2a7af24a51cd9b9f153c7744b310b

kokoro/gcp_ubuntu/release-nightly.cfg

@@ -2,8 +2,9 @@
 build_file: "repo/kokoro/gcp_ubuntu/run_build.sh"
 
 action {
-  # Upload only the runsc binary.
+  # Upload only the runsc binary. It may be in multiple paths, so we must use
+  # the wildcard.
   define_artifacts {
-    regex: "runsc"
+    regex: "**/runsc"
   }
 }

kokoro/gcp_ubuntu/run_build.sh

@@ -31,5 +31,10 @@ cd git/repo
 # Build runsc.
 bazel build //runsc
 
-# Move the built binary to the top of the artifacts directory.
-mv bazel-bin/runsc/linux_amd64_pure_stripped/runsc "${KOKORO_ARTIFACTS_DIR}"/runsc
+# Move the runsc binary into "latest" directory, and also a directory with the
+# current date.
+latest_dir="${KOKORO_ARTIFACTS_DIR}"/nightly/latest
+today_dir="${KOKORO_ARTIFACTS_DIR}"/nightly/"$(date -Idate)"
+mkdir -p "${latest_dir}" "${today_dir}"
+cp bazel-bin/runsc/linux_amd64_pure_stripped/runsc "${latest_dir}"
+cp bazel-bin/runsc/linux_amd64_pure_stripped/runsc "${today_dir}"