Mock btrfs hook in non linux platforms like darwin

worker/btrfs_snapshot_hook_nolinux.go

@@ -0,0 +1,30 @@
+// +build !linux
+
+package worker
+
+type btrfsSnapshotHook struct {
+}
+
+func newBtrfsSnapshotHook(provider mirrorProvider, snapshotPath string, mirror mirrorConfig) *btrfsSnapshotHook {
+	return &btrfsSnapshotHook{}
+}
+
+func (h *btrfsSnapshotHook) postExec() error {
+	return nil
+}
+
+func (h *btrfsSnapshotHook) postFail() error {
+	return nil
+}
+
+func (h *btrfsSnapshotHook) postSuccess() error {
+	return nil
+}
+
+func (h *btrfsSnapshotHook) preExec() error {
+	return nil
+}
+
+func (h *btrfsSnapshotHook) preJob() error {
+	return nil
+}