Parallelize builds
diff --git a/ci/build-release-matrix b/ci/build-release-matrix
new file mode 100755
index 0000000..25e689d
--- /dev/null
+++ b/ci/build-release-matrix
@@ -0,0 +1,10 @@
+#!/usr/bin/env python3
+
+import glob
+import sys
+import json
+
+
+json.dump([
+    r.split('/')[-1] for r in glob.glob('images/openstack/releases/*')
+], sys.stdout, separators=(',', ':'))