Allow to skip go test

`make test` has been broken since #300 was merged and fixing it is going to
take time (see #310 for details). It is a problem for local development since
the `test` target is a prequisite for `docker-build` in the makefile.

Add a variable to control whether `go test` should run when the `test`
target is invoked.

 $ make test SKIP_TESTS=   # Run `go test` when unset

 $ make test SKIP_TESTS=1  # Don't run `go test` when set

Default is unset.

Signed-off-by: Greg Kurz <groug@kaod.org>

Makefile

@@ -76,6 +76,12 @@ space := $() $()
 comma := ,
 GOFLAGS := -tags=$(subst $(space),$(comma),$(strip $(BUILTIN_CLOUD_PROVIDERS)))
 
+#
+# If SKIP_TESTS is set, the test target will *not* run `go test`.
+# This is to be able to temporarily work around test failures when doing
+# local development.
+SKIP_TESTS =
+
 .PHONY: all
 all: build
 
@@ -116,9 +122,13 @@ vet: ## Run go vet against code.
 
 .PHONY: test
 test: manifests generate fmt vet envtest ## Run tests.
+ifneq (, $(SKIP_TESTS))
+	@echo Skipping tests. Unset SKIP_TESTS to actually run them.
+else
 	KUBEBUILDER_ASSETS="$(shell $(ENVTEST) use $(ENVTEST_K8S_VERSION) --bin-dir $(LOCALBIN) -p path)" go test $(GOFLAGS) ./... -coverprofile cover.out
 	# set write flag on created folder, so that we can clean it up
 	chmod +w $(LOCALBIN)/k8s/$(ENVTEST_K8S_VERSION)*
+endif
 
 ##@ Build