cmd/dist: run commands in $GOROOT/src not $GOROOT when possible

The go command prints paths in errors relative to its current directory.
Since all.bash and run.bash are run in $GOROOT/src, prefer to run
the go command, so that the relative paths are correct.

Before this CL, running all.bash in $GOROOT/src:

	##### Testing race detector
	# net/http
	src/net/http/transport.go:1257: cannot take the address of <node EFACE>

This is wrong (or at least less useful) because there is no $GOROOT/src/src/net/http directory.

Change-Id: I0c0d52c22830d79b3715f51a6329a3d33de52a72
Reviewed-on: https://go-review.googlesource.com/9157Reviewed-by: Rob Pike <r@golang.org>

src/cmd/dist/test.go

@@ -200,7 +200,7 @@ func (t *tester) registerTests() {
 			name:    testName,
 			heading: "GOMAXPROCS=2 runtime -cpu=1,2,4",
 			fn: func() error {
-				cmd := t.dirCmd(".", "go", "test", "-short", t.timeout(300), "runtime", "-cpu="+cpu)
+				cmd := t.dirCmd("src", "go", "test", "-short", t.timeout(300), "runtime", "-cpu="+cpu)
 				// We set GOMAXPROCS=2 in addition to -cpu=1,2,4 in order to test runtime bootstrap code,
 				// creation of first goroutines and first garbage collections in the parallel setting.
 				cmd.Env = mergeEnvLists([]string{"GOMAXPROCS=2"}, os.Environ())
@@ -214,7 +214,7 @@ func (t *tester) registerTests() {
 		name:    "sync_cpu",
 		heading: "sync -cpu=10",
 		fn: func() error {
-			return t.dirCmd(".", "go", "test", "sync", "-short", t.timeout(120), "-cpu=10").Run()
+			return t.dirCmd("src", "go", "test", "sync", "-short", t.timeout(120), "-cpu=10").Run()
 		},
 	})
 
@@ -309,7 +309,7 @@ func (t *tester) registerTests() {
 			name:    "api",
 			heading: "API check",
 			fn: func() error {
-				return t.dirCmd(".", "go", "run", filepath.Join(t.goroot, "src/cmd/api/run.go")).Run()
+				return t.dirCmd("src", "go", "run", filepath.Join(t.goroot, "src/cmd/api/run.go")).Run()
 			},
 		})
 	}
@@ -573,18 +573,18 @@ func (t *tester) raceDetectorSupported() bool {
 }
 
 func (t *tester) raceTest() error {
-	if err := t.dirCmd(".", "go", "test", "-race", "-i", "runtime/race", "flag", "os/exec").Run(); err != nil {
+	if err := t.dirCmd("src", "go", "test", "-race", "-i", "runtime/race", "flag", "os/exec").Run(); err != nil {
 		return err
 	}
-	if err := t.dirCmd(".", "go", "test", "-race", "-run=Output", "runtime/race").Run(); err != nil {
+	if err := t.dirCmd("src", "go", "test", "-race", "-run=Output", "runtime/race").Run(); err != nil {
 		return err
 	}
-	if err := t.dirCmd(".", "go", "test", "-race", "-short", "flag", "os/exec").Run(); err != nil {
+	if err := t.dirCmd("src", "go", "test", "-race", "-short", "flag", "os/exec").Run(); err != nil {
 		return err
 	}
 	if t.extLink() {
 		// Test with external linking; see issue 9133.
-		if err := t.dirCmd(".", "go", "test", "-race", "-short", "-ldflags=-linkmode=external", "flag", "os/exec").Run(); err != nil {
+		if err := t.dirCmd("src", "go", "test", "-race", "-short", "-ldflags=-linkmode=external", "flag", "os/exec").Run(); err != nil {
 			return err
 		}
 	}