Move hftest headers to a test inc directory.

Other common test headers can also go under this directory, rather
than having shared 'inc' directories scattered around the test source
tree.

Change-Id: I990bdc11ad08bd44377ac2e064c566f552ff22b5
diff --git a/test/vmapi/primary_with_secondaries/interrupts.c b/test/vmapi/primary_with_secondaries/interrupts.c
index e315b9e..ac64049 100644
--- a/test/vmapi/primary_with_secondaries/interrupts.c
+++ b/test/vmapi/primary_with_secondaries/interrupts.c
@@ -20,8 +20,8 @@
 
 #include "vmapi/hf/call.h"
 
-#include "hftest.h"
 #include "primary_with_secondary.h"
+#include "test/hftest.h"
 #include "util.h"
 
 /**