cmd/go: fix failing tests since vet was moved from x/tools

Change-Id: I3276a118ced78f3efd8f1bc5fb8b8fa2fde52496
Reviewed-on: https://go-review.googlesource.com/21704Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/go_test.go

@@ -2320,8 +2320,7 @@ func TestGoVetWithExternalTests(t *testing.T) {
 	tg := testgo(t)
 	defer tg.cleanup()
 	tg.makeTempdir()
-	tg.setenv("GOPATH", tg.path("."))
-	tg.run("get", "golang.org/x/tools/cmd/vet")
+	tg.run("install", "cmd/vet")
 	tg.setenv("GOPATH", filepath.Join(tg.pwd(), "testdata"))
 	tg.runFail("vet", "vetpkg")
 	tg.grepBoth("missing argument for Printf", "go vet vetpkg did not find missing argument for Printf")
@@ -2333,8 +2332,7 @@ func TestGoVetWithTags(t *testing.T) {
 	tg := testgo(t)
 	defer tg.cleanup()
 	tg.makeTempdir()
-	tg.setenv("GOPATH", tg.path("."))
-	tg.run("get", "golang.org/x/tools/cmd/vet")
+	tg.run("install", "cmd/vet")
 	tg.setenv("GOPATH", filepath.Join(tg.pwd(), "testdata"))
 	tg.runFail("vet", "-tags", "tagtest", "vetpkg")
 	tg.grepBoth(`c\.go.*wrong number of args for format`, "go get vetpkg did not run scan tagged file")