tubes: fix build of unit test; set include path for now

Later we would want to move headers if they are not used outside.

Change-Id: I863f6f00254b335af563598a195aea01595f6c99

tubes/CppunitTest_tubes_test.mk

@@ -30,6 +30,11 @@ $(eval $(call gb_CppunitTest_add_exception_objects,tubes_test, \
 	tubes/qa/test_manager \
 ))
 
+$(eval $(call gb_CppunitTest_set_include,tubes_test, \
+	-I$(SRCDIR)/tubes/inc \
+	$$(INCLUDE) \
+))
+
 $(eval $(call gb_CppunitTest_use_packages,tubes_test,tubes_inc))
 
 $(eval $(call gb_CppunitTest_use_library_objects,tubes_test,tubes))