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_printer_yang.c b/tests/utests/schema/test_printer_yang.c
index feea18e..24e8b31 100644
--- a/tests/utests/schema/test_printer_yang.c
+++ b/tests/utests/schema/test_printer_yang.c
@@ -20,9 +20,9 @@
 #include <stdio.h>
 #include <string.h>
 
-#include "../../src/context.h"
-#include "../../src/printer.h"
-#include "../../src/printer_schema.h"
+#include "context.h"
+#include "printer.h"
+#include "printer_schema.h"
 
 #define BUFSIZE 1024
 char logbuf[BUFSIZE] = {0};