Implement DatasetMapping + basic ZFS list functionality.

zfs/test_helpers/exec_mapping_good.sh

@@ -0,0 +1,18 @@
+#!/bin/bash
+
+
+
+while read line # we know this is not always correct...
+do
+    if [[ "$line" =~ nomap* ]]; then
+        echo "NOMAP"
+        continue
+    fi
+
+    echo "didmap/${line}"
+
+    if [ "$1" == "stop" ]; then
+        break
+    fi
+
+done

zfs/test_helpers/zfs_failer.sh

@@ -0,0 +1,3 @@
+#!/bin/sh
+echo "error: this is a mock" 1>&2
+exit 1