tests CHANGE headers includes cleanup

Set necessary include directories instead of including library headers
in tests via relative path (which cause problems when building in
some nonstandard build directories).
diff --git a/tests/utests/schema/test_parser_yin.c b/tests/utests/schema/test_parser_yin.c
index d2576b9..737d2d5 100644
--- a/tests/utests/schema/test_parser_yin.c
+++ b/tests/utests/schema/test_parser_yin.c
@@ -21,13 +21,13 @@
 #include <string.h>
 #include <stdbool.h>
 
-#include "../../../src/common.h"
-#include "../../../src/tree_schema.h"
-#include "../../../src/tree_schema_internal.h"
-#include "../../../src/parser_internal.h"
-#include "../../../src/parser_yin.h"
-#include "../../../src/xml.h"
-#include "../../../src/xpath.h"
+#include "common.h"
+#include "parser_internal.h"
+#include "parser_yin.h"
+#include "tree_schema.h"
+#include "tree_schema_internal.h"
+#include "xml.h"
+#include "xpath.h"
 
 /* prototypes of static functions */
 void lysp_ext_instance_free(struct ly_ctx *ctx, struct lysp_ext_instance *ext);