build: Enable gometalinter "gosimple" check, improve build.go

lib/db/blockmap_test.go

@@ -58,10 +58,7 @@ func setup() (*Instance, *BlockFinder) {
 func dbEmpty(db *Instance) bool {
 	iter := db.NewIterator(util.BytesPrefix([]byte{KeyTypeBlock}), nil)
 	defer iter.Release()
-	if iter.Next() {
-		return false
-	}
-	return true
+	return !iter.Next()
 }
 
 func TestBlockMapAddUpdateWipe(t *testing.T) {

lib/db/concurrency_test.go

@@ -4,7 +4,8 @@
 // License, v. 2.0. If a copy of the MPL was not distributed with this file,
 // You can obtain one at http://mozilla.org/MPL/2.0/.
 
-// +build ignore // this  is a really tedious test for an old issue
+// this  is a really tedious test for an old issue
+// +build ignore
 
 package db_test