e2e: allow unknown providers with a warning

The E2E refactoring tightened the sanity checking of the --provider
parameter such that it only allowed known providers. That seemed to
make sense because it catches typos, but it turned out that various
callers depended on the "accept arbitrary provider value" behavior,
therefore it gets restored.

test/e2e/framework/BUILD

@@ -134,6 +134,7 @@ go_library(
         "//vendor/github.com/onsi/ginkgo/config:go_default_library",
         "//vendor/github.com/onsi/gomega:go_default_library",
         "//vendor/github.com/onsi/gomega/types:go_default_library",
+        "//vendor/github.com/pkg/errors:go_default_library",
         "//vendor/github.com/prometheus/common/expfmt:go_default_library",
         "//vendor/github.com/prometheus/common/model:go_default_library",
         "//vendor/golang.org/x/crypto/ssh:go_default_library",

test/e2e/framework/provider.go

@@ -18,8 +18,11 @@ package framework
 
 import (
 	"fmt"
+	"os"
 	"sync"
 
+	"github.com/pkg/errors"
+
 	"k8s.io/api/core/v1"
 	clientset "k8s.io/client-go/kubernetes"
 )
@@ -66,7 +69,7 @@ func SetupProviderConfig(providerName string) (ProviderInterface, error) {
 	defer mutex.Unlock()
 	factory, ok := providers[providerName]
 	if !ok {
-		return nil, fmt.Errorf("The provider %s is unknown.", providerName)
+		return nil, errors.Wrapf(os.ErrNotExist, "The provider %s is unknown.", providerName)
 	}
 	provider, err := factory()
 

test/e2e/framework/test_context.go

@@ -25,6 +25,7 @@ import (
 
 	"github.com/golang/glog"
 	"github.com/onsi/ginkgo/config"
+	"github.com/pkg/errors"
 	utilflag "k8s.io/apiserver/pkg/util/flag"
 	restclient "k8s.io/client-go/rest"
 	"k8s.io/client-go/tools/clientcmd"
@@ -366,7 +367,20 @@ func AfterReadingAllFlags(t *TestContextType) {
 	// Make sure that all test runs have a valid TestContext.CloudConfig.Provider.
 	var err error
 	TestContext.CloudConfig.Provider, err = SetupProviderConfig(TestContext.Provider)
+	if err == nil {
+		return
+	}
+	if !os.IsNotExist(errors.Cause(err)) {
+		Failf("Failed to setup provider config: %v", err)
+	}
+	// We allow unknown provider parameters for historic reasons. At least log a
+	// warning to catch typos.
+	// TODO (https://github.com/kubernetes/kubernetes/issues/70200):
+	// - remove the fallback for unknown providers
+	// - proper error message instead of Failf (which panics)
+	glog.Warningf("Unknown provider %q, proceeding as for --provider=skeleton.", TestContext.Provider)
+	TestContext.CloudConfig.Provider, err = SetupProviderConfig("skeleton")
 	if err != nil {
-		Failf("Failed to setup provide r config: %v", err)
+		Failf("Failed to setup fallback skeleton provider config: %v", err)
 	}
 }