tests: ensure factor tests can be regenerated

* tests/local.mk (factor-tests:) Add -f to the mv command that
replaces any existing generated tests.  This is required to avoid
prompts when root initially generates the tests, and they subsequently
need to be regenerated by a non root user.

tests/local.mk

@@ -658,7 +658,7 @@ $(factor_tests): $(tf)/run.sh $(tf)/create-test.sh
 	$(AM_V_at)$(SHELL) $(srcdir)/$(tf)/create-test.sh $@ \
 	  $(srcdir)/$(tf)/run.sh > $@-t
 	$(AM_V_at)chmod a+x $@-t
-	$(AM_V_at)mv $@-t $@
+	$(AM_V_at)mv -f $@-t $@
 
 CLEANFILES += $(factor_tests)