cmd/go: skipping relative paths on go test -i ./...

Fixes #3896.

R=rsc, rogpeppe, r
CC=golang-dev
https://golang.org/cl/6457075

src/cmd/go/test.bash

@@ -76,6 +76,12 @@ if ! ./testgo test ./testdata/testimport; then
 	ok=false
 fi
 
+# Test installation with relative imports.
+if ! ./testgo test -i ./testdata/testimport; then
+    echo "go test -i ./testdata/testimport failed"
+    ok=false
+fi
+
 # Test tests with relative imports in packages synthesized
 # from Go files named on the command line.
 if ! ./testgo test ./testdata/testimport/*.go; then

src/cmd/go/test.go

@@ -276,8 +276,10 @@ func runTest(cmd *Command, args []string) {
 
 		all := []string{}
 		for path := range deps {
+			if !build.IsLocalImport(path) {
 				all = append(all, path)
 			}
+		}
 		sort.Strings(all)
 
 		a := &action{}