build: move e2e dependencies into e2e/go.mod

Several packages are only used while running the e2e suite. These
packages are less important to update, as the they can not influence the
final executable that is part of the Ceph-CSI container-image.

By moving these dependencies out of the main Ceph-CSI go.mod, it is
easier to identify if a reported CVE affects Ceph-CSI, or only the
testing (like most of the Kubernetes CVEs).

Signed-off-by: Niels de Vos <ndevos@ibm.com>

e2e/vendor/k8s.io/apiserver/pkg/util/flushwriter/doc.go

@@ -0,0 +1,19 @@
+/*
+Copyright 2014 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package flushwriter implements a wrapper for a writer that flushes on every
+// write if that writer implements the io.Flusher interface
+package flushwriter // import "k8s.io/apiserver/pkg/util/flushwriter"

e2e/vendor/k8s.io/apiserver/pkg/util/flushwriter/writer.go

@@ -0,0 +1,53 @@
+/*
+Copyright 2014 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package flushwriter
+
+import (
+	"io"
+	"net/http"
+)
+
+// Wrap wraps an io.Writer into a writer that flushes after every write if
+// the writer implements the Flusher interface.
+func Wrap(w io.Writer) io.Writer {
+	fw := &flushWriter{
+		writer: w,
+	}
+	if flusher, ok := w.(http.Flusher); ok {
+		fw.flusher = flusher
+	}
+	return fw
+}
+
+// flushWriter provides wrapper for responseWriter with HTTP streaming capabilities
+type flushWriter struct {
+	flusher http.Flusher
+	writer  io.Writer
+}
+
+// Write is a FlushWriter implementation of the io.Writer that sends any buffered
+// data to the client.
+func (fw *flushWriter) Write(p []byte) (n int, err error) {
+	n, err = fw.writer.Write(p)
+	if err != nil {
+		return
+	}
+	if fw.flusher != nil {
+		fw.flusher.Flush()
+	}
+	return
+}