Add luci-auth tool

I needed it to test changes to the artifacts tool

Change-Id: I8c1106cd4c88fc741147028f1faaad1d7b4efd21
diff --git a/cipd.ensure b/cipd.ensure
index aa9150b..67f2e72 100644
--- a/cipd.ensure
+++ b/cipd.ensure
@@ -26,6 +26,9 @@
 # LogDog CLI client
 infra/tools/luci/logdog/logdog/${platform} git_revision:4dc2c26daea364a8ea5c150f670b1999d63005a1
 
+# LUCI auth tool
+infra/tools/luci-auth/${platform} git_revision:4dc2c26daea364a8ea5c150f670b1999d63005a1
+
 # Lucicfg tool
 infra/tools/luci/lucicfg/${platform}  git_revision:4dc2c26daea364a8ea5c150f670b1999d63005a1