tests: use buffer engine for elm_suite if engine is not specified

this should add some consistency to tests

Signed-off-by: Mike Blumenkrantz <zmike@osg.samsung.com>

src/tests/elementary/elm_suite.c

@@ -98,8 +98,9 @@ main(int argc, char **argv)
 
 #ifdef NEED_RUN_IN_TREE
    putenv("EFL_RUN_IN_TREE=1");
-   putenv("EFL_RUN_IN_TREE=1");
 #endif
+   if (!getenv("ELM_ENGINE"))
+     putenv("ELM_ENGINE=buffer");
 
    failed_count = _efl_suite_build_and_run(argc - 1, (const char **)argv + 1,
                                            "Elementary", etc);