test: enable unit tests under test/e2e

The test/e2e directory contains several unit tests that should run as part of
"make test":

./test/e2e/chaosmonkey/chaosmonkey_test.go
./test/e2e/storage/external/external_test.go
./test/e2e/storage/utils/utils_test.go
./test/e2e/framework/log_test.go
./test/e2e/framework/testfiles/testfiles_test.go
./test/e2e/framework/timer/timer_test.go
./test/e2e/framework/node/wait_test.go
./test/e2e/framework/pod/resource_test.go
./test/e2e/framework/config/config_test.go
./test/e2e/framework/ingress/ingress_utils_test.go
./test/e2e/framework/providers/gce/firewall_test.go

Because they were excluded by "./test/e2e/*", some of them became outdated.

./test/e2e/e2e_test.go is the only test that needs to be excluded because it is
the E2E test suite that depends on a functional cluster.

hack/make-rules/test.sh

@@ -44,7 +44,7 @@ kube::test::find_dirs() {
           -o -path './output/*' \
           -o -path './release/*' \
           -o -path './target/*' \
-          -o -path './test/e2e/*' \
+          -o -path './test/e2e/e2e_test.go' \
           -o -path './test/e2e_node/*' \
           -o -path './test/e2e_kubeadm/*' \
           -o -path './test/integration/*' \