e2e: modular framework

Not all users of the E2E framework want to run cloud-provider specific
tests. By splitting out the code it becomes possible to decide in
a E2E test suite which providers are supported.

This is achieved in two ways:
- the framework calls certain functions through a provider
  interface instead of calling specific cloud provider functions
  directly
- tests that are cloud-provider specific directly import the
  new provider packages

The ingress test utilities are only needed by a few tests. Splitting
them out into a separate package makes the framework simpler for test
suites not using those tests.

Fixes: #66649

test/e2e_node/e2e_node_suite_test.go

@@ -71,6 +71,7 @@ func init() {
 	// It seems that someone is using flag.Parse() after init() and TestMain().
 	// TODO(random-liu): Find who is using flag.Parse() and cause errors and move the following logic
 	// into TestContext.
+	// TODO(pohly): remove RegisterNodeFlags from test_context.go enable Viper config support here?
 }
 
 func TestMain(m *testing.M) {