generate jsonnet-bundler binary if it's not available

Also locks jsonnet-bundler to version v0.2.0

scripts/tools.go

@@ -0,0 +1,9 @@
+//+build tools
+
+// Package tools tracks dependencies for tools that used in the build process.
+// See https://github.com/golang/go/wiki/Modules
+package tools
+
+import (
+	_ "github.com/jsonnet-bundler/jsonnet-bundler/cmd/jb"
+)