test: Add findmnt package

When testing mounts we can use findmnt --json output to parse the output
cleanly. The package provides only ParseOutput() now, but it can be
extended later to run the findmnt command.

Author: nirs

test/integration/findmnt/findmnt.go

@@ -0,0 +1,42 @@
+//go:build integration
+
+/*
+Copyright 2025 The Kubernetes Authors All rights reserved.
+
+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 parse findmnt command results.
+package findmnt
+
+import "encoding/json"
+
+type Filesystem struct {
+	Target  string `json:"target"`
+	Source  string `json:"source"`
+	FSType  string `json:"fstype"`
+	Options string `json:"options"`
+}
+
+type Result struct {
+	Filesystems []Filesystem `json:"filesystems"`
+}
+
+// ParseOutput parse findmnt output.
+func ParseOutput(output []byte) (*Result, error) {
+	r := &Result{}
+	if err := json.Unmarshal(output, r); err != nil {
+		return nil, err
+	}
+	return r, nil
+}