Set query classifier with an absolute path in tests

Setting the query classifier with an absolute path makes it easier to
manage test setup without having to manually resolve the relative path to
the query classifier from the test source directory.

server/core/test/test_utils.h

@@ -21,6 +21,8 @@
 #include <maxscale/log_manager.h>
 #include <maxscale/config.h>
 #include <maxscale/query_classifier.h>
+#include <maxscale/paths.h>
+#include <maxscale/alloc.h>
 
 #include <sys/stat.h>
 
@@ -38,6 +40,7 @@ void init_test_env(char *path)
         exit(1);
     }
     dcb_global_init();
+    set_libdir(MXS_STRDUP(TEST_DIR "/query_classifier/qc_sqlite/"));
     qc_setup(NULL, NULL);
     qc_process_init(QC_INIT_BOTH);
     poll_init();