cmd/go: convert TestIssue17119 to the script test framework

It's already parallel, but we might as well convert it and
get rid of the testdata/src dircetory completely.

Updates #36320

Change-Id: I75e335b32d64a8ddedd65e4337949b729c9e0fbe
Reviewed-on: https://go-review.googlesource.com/c/go/+/212877
Run-TryBot: Michael Matloob <[email protected]>
Reviewed-by: Jay Conrod <[email protected]>

src/cmd/go/go_test.go

@@ -3504,18 +3504,6 @@ func TestGoGetUpdateAllDoesNotTryToLoadDuplicates(t *testing.T) {
 	tg.grepStderrNot("duplicate loads of", "did not remove old packages from cache")
 }
 
-// Issue 17119 more duplicate load errors
-func TestIssue17119(t *testing.T) {
-	testenv.MustHaveExternalNetwork(t)
-
-	tg := testgo(t)
-	defer tg.cleanup()
-	tg.parallel()
-	tg.setenv("GOPATH", filepath.Join(tg.pwd(), "testdata"))
-	tg.runFail("build", "dupload")
-	tg.grepBothNot("duplicate load|internal error", "internal error")
-}
-
 func TestBinaryOnlyPackages(t *testing.T) {
 	tooSlow(t)
 

src/cmd/go/testdata/script/gopath_vendor_dup_err.txt

@@ -0,0 +1,24 @@
+[!net] skip
+
+# Issue 17119: Test more duplicate load errors.
+! go build dupload
+! stderr 'duplicate load|internal error'
+stderr 'dupload/vendor/p must be imported as p'
+
+-- dupload/dupload.go --
+package main
+
+import (
+	_ "dupload/p2"
+	_ "p"
+)
+
+func main() {}
+-- dupload/p/p.go --
+package p
+-- dupload/p2/p2.go --
+package p2
+
+import _ "dupload/vendor/p"
+-- dupload/vendor/p/p.go --
+package p