all: fix vet nits

Fixes these vet complaints:

net/error_test.go:254: unrecognized printf flag for verb 'T': '#'
os/os_test.go:1067: arg mt for printf verb %d of wrong type: time.Time
runtime/debug/garbage_test.go:83: arg dt for printf verb %d of wrong type: time.Time

Change-Id: I0e986712a4b083b75fb111e687e424d06a85a47b
Reviewed-on: https://go-review.googlesource.com/33167
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/error_test.go

@@ -251,7 +251,7 @@ func TestDialAddrError(t *testing.T) {
 		operr := err.(*OpError).Err
 		aerr, ok := operr.(*AddrError)
 		if !ok {
-			t.Errorf("%s: %v is %#T, want *AddrError", op, err, operr)
+			t.Errorf("%s: %v is %T, want *AddrError", op, err, operr)
 			continue
 		}
 		want := tt.lit

src/os/os_test.go

@@ -1064,7 +1064,7 @@ func testChtimes(t *testing.T, name string) {
 	}
 
 	if !pmt.Before(mt) {
-		t.Errorf("ModTime didn't go backwards; was=%d, after=%d", mt, pmt)
+		t.Errorf("ModTime didn't go backwards; was=%v, after=%v", mt, pmt)
 	}
 }
 

src/runtime/debug/garbage_test.go

@@ -80,7 +80,7 @@ func TestReadGCStats(t *testing.T) {
 	for i := 0; i < n; i++ {
 		dt := stats.PauseEnd[i]
 		if dt.UnixNano() != int64(mstats.PauseEnd[off]) {
-			t.Errorf("stats.PauseEnd[%d] = %d, want %d", i, dt, mstats.PauseEnd[off])
+			t.Errorf("stats.PauseEnd[%d] = %d, want %d", i, dt.UnixNano(), mstats.PauseEnd[off])
 		}
 		off = (off + len(mstats.PauseEnd) - 1) % len(mstats.PauseEnd)
 	}