tests CHANGE rename config.h to tests_config.h

Make the tests' config header name clearly connected with tests. The
config.h is supposed to be connected with sources.
diff --git a/tests/utests/utests.h b/tests/utests/utests.h
index c3bfb73..fa686d3 100644
--- a/tests/utests/utests.h
+++ b/tests/utests/utests.h
@@ -29,7 +29,7 @@
 #include "libyang.h"
 #include "plugins_internal.h"
 #include "plugins_types.h"
-#include "tests/config.h"
+#include "tests_config.h"
 #include "tree_schema_internal.h"
 
 /**