cmd/go: small code reorganization

covermode is not passed to 6.out, so it should not be grouped
with the flags that are. Move it to the "local" section.

Change-Id: Id487898962e7ab7adf98b0854c2f1802116bec11
Reviewed-on: https://go-review.googlesource.com/8132Reviewed-by: Minux Ma <minux@golang.org>

src/cmd/go/testflag.go

@@ -30,6 +30,7 @@ var testFlagDefn = []*testFlagSpec{
 	// local.
 	{name: "c", boolVar: &testC},
 	{name: "cover", boolVar: &testCover},
+	{name: "covermode"},
 	{name: "coverpkg"},
 	{name: "o"},
 
@@ -53,7 +54,6 @@ var testFlagDefn = []*testFlagSpec{
 	{name: "bench", passToTest: true},
 	{name: "benchmem", boolVar: new(bool), passToTest: true},
 	{name: "benchtime", passToTest: true},
-	{name: "covermode"},
 	{name: "coverprofile", passToTest: true},
 	{name: "cpu", passToTest: true},
 	{name: "cpuprofile", passToTest: true},