channeldb: move makeTestDB out of test to make it available for other tests

This commit moves makeTestDB to db.go and exports it so that we'll be
able to use this function in other unit tests to make them testable with
etcd if needed.

channeldb/nodes_test.go

@@ -13,7 +13,7 @@ import (
 func TestLinkNodeEncodeDecode(t *testing.T) {
 	t.Parallel()
 
-	cdb, cleanUp, err := makeTestDB()
+	cdb, cleanUp, err := MakeTestDB()
 	if err != nil {
 		t.Fatalf("unable to make test database: %v", err)
 	}
@@ -110,7 +110,7 @@ func TestLinkNodeEncodeDecode(t *testing.T) {
 func TestDeleteLinkNode(t *testing.T) {
 	t.Parallel()
 
-	cdb, cleanUp, err := makeTestDB()
+	cdb, cleanUp, err := MakeTestDB()
 	if err != nil {
 		t.Fatalf("unable to make test database: %v", err)
 	}