fix(deisctl): avoid stdout issues in tests

Some unit tests will fail with GOMAXPROCS > 1, so this change
allows `make test-unit` to pass until there is a proper fix.

Author: mboersma

deisctl/Makefile

@@ -41,4 +41,5 @@ test-style:
 	$(GOLINT) ./...
 
 test-unit:
-	$(GOTEST) ./...
+# TODO: remove GOMAXPROCS=1 when concurrent stdout issues are fixed
+	GOMAXPROCS=1 $(GOTEST) ./...