GREENTEA: init trace if trace is enabled in json

Author: jeromecoutant

features/frameworks/greentea-client/source/greentea_test_env.cpp

@@ -23,7 +23,7 @@
 #include "greentea-client/test_env.h"
 #include "greentea-client/greentea_serial.h"
 #include "greentea-client/greentea_metrics.h"
-
+#include "mbed_trace.h"
 
 /**
  *   Generic test suite transport protocol keys
@@ -84,6 +84,10 @@ void _GREENTEA_SETUP_COMMON(const int timeout, const char *host_test_name, char
         }
     }
 
+#ifdef MBED_CONF_MBED_TRACE_ENABLE
+    mbed_trace_init();
+#endif
+
     greentea_notify_version();
     greentea_notify_timeout(timeout);
     greentea_notify_hosttest(host_test_name);