Add go environment vendor directory support (#781)

* Add go environment vendor directory support
* Use symbolink instead of copying files to gopath
* Add go vendor example package & test

examples/go/vendor-example/vendor/go/vendordir/test/test.go

@@ -0,0 +1,5 @@
+package test
+
+func Test() string {
+    return "vendor hello world"
+}