make: use existing unit-race command

This allows us to specify a pkg= and case= argument to the
flake-unit-race test.

Author: guggero

Makefile

@@ -230,7 +230,7 @@ flake-unit-trace:
 
 flake-unit-race:
 	@$(call print, "Flake hunting races in unit tests.")
-	while [ $$? -eq 0 ]; do $(GOLIST) | $(XARGS) env CGO_ENABLED=1 GORACE="history_size=7 halt_on_errors=1" $(GOTEST) -race -test.timeout=20m -count=1; done
+	while [ $$? -eq 0 ]; do make unit-race nocache=1; done
 
 # =============
 # FUZZING