http2: reduce alloc-heavy init

Moves test cases into the test where they're used, to remove
distractions when profiling unrelated tests.

Also this is my style preference, to remove globals and reduce the
scope of variables.

Change-Id: Ie9cd41b16aad9acf5e210f1fb6f19a7fce52180d
Reviewed-on: https://go-review.googlesource.com/20996Reviewed-by: Andrew Gerrand <adg@golang.org>

http2/transport_test.go

@@ -326,10 +326,11 @@ func randString(n int) string {
 	return string(b)
 }
 
-var bodyTests = []struct {
+func TestTransportBody(t *testing.T) {
+	bodyTests := []struct {
 		body         string
 		noContentLen bool
-}{
+	}{
 		{body: "some message"},
 		{body: "some message", noContentLen: true},
 		{body: ""},
@@ -345,9 +346,8 @@ var bodyTests = []struct {
 		{body: randString(1<<20 - 1)},
 		{body: randString(1 << 20)},
 		{body: randString(1<<20 + 2)},
-}
+	}
 
-func TestTransportBody(t *testing.T) {
 	type reqInfo struct {
 		req   *http.Request
 		slurp []byte