prometheus-node-exporter-lua: export static files

Print all files from /var/prometheus/*.prom. This behaviour allow users
to add metrics with non-lua scripts.

Signed-off-by: Paul Spooren <spooren@informatik.uni-leipzig.de>

utils/prometheus-node-exporter-lua/files/usr/lib/lua/prometheus-collectors/textfile.lua

@@ -0,0 +1,11 @@
+#!/usr/bin/lua
+
+local fs = require "nixio.fs"
+
+local function scrape()
+  for metrics in fs.glob("/var/prometheus/*.prom") do
+    output(get_contents(metrics), '\n')
+  end
+end
+
+return { scrape = scrape }