feat(templater): Added support for file include

Adds a 'fileContent' template function to insert the literal contents
of a file specified in the template.

Signed-off-by: Niklas Wik <niklas.wik@nokia.com>

templater/fromfile.go

@@ -0,0 +1,24 @@
+// Copyright (C) 2017  Niklas Wik <niklas.wik@nokia.com>
+//
+// This file is part of Kontemplate.
+//
+// Kontemplate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+package templater
+
+import (
+	"io/ioutil"
+)
+
+//GetFromFile returns file content as string
+func GetFromFile(file string) (string, error) {
+
+	data, err := ioutil.ReadFile(file)
+	if err != nil {
+		return "", err
+	}
+	return string(data), nil
+}

templater/templater.go

@@ -193,6 +193,7 @@ func templateFuncs() template.FuncMap {
 	}
 	m["passLookup"] = GetFromPass
 	m["lookupIPAddr"] = GetIPsFromDNS
+	m["fileContent"] = GetFromFile
 
 	return m
 }