ZTS: zfs_program_json

As of Python 3.5 the default behavior of json.tool was changed to
preserve the input order rather than lexical order.  The test case
expects the output to be sorted so apply the --sort-keys option
to the json.tool command when using Python 3.5 and the option is
supported.

    https://docs.python.org/3/library/json.html#module-json.tool

Reviewed-by: Kjeld Schouten <kjeld@schouten-lebbing.nl>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #9774

tests/zfs-tests/tests/functional/cli_root/zfs_program/zfs_program_json.ksh

@@ -91,14 +91,28 @@ typeset -a pos_cmds_out=(
         }
     }
 }")
+
+#
+# N.B. json.tool is needed to guarantee consistent ordering of fields,
+# sed is needed to trim trailing space in CentOS 6's json.tool output
+#
+# As of Python 3.5 the behavior of json.tool changed to keep the order
+# the same as the input and the --sort-keys option was added.  Detect when
+# --sort-keys is supported and apply the option to ensure the expected order.
+#
+if python -m json.tool --sort-keys <<< "{}"; then
+	JSON_TOOL_CMD="python -m json.tool --sort-keys"
+else
+	JSON_TOOL_CMD="python -m json.tool"
+fi
+
 typeset -i cnt=0
 typeset cmd
 for cmd in ${pos_cmds[@]}; do
 	log_must zfs program $TESTPOOL $TESTZCP $TESTDS $cmd 2>&1
 	log_must zfs program -j $TESTPOOL $TESTZCP $TESTDS $cmd 2>&1
-	# json.tool is needed to guarantee consistent ordering of fields
-	# sed is needed to trim trailing space in CentOS 6's json.tool output
-	OUTPUT=$(zfs program -j $TESTPOOL $TESTZCP $TESTDS $cmd 2>&1 | python -m json.tool | sed 's/[[:space:]]*$//')
+	OUTPUT=$(zfs program -j $TESTPOOL $TESTZCP $TESTDS $cmd 2>&1 |
+	    $JSON_TOOL_CMD | sed 's/[[:space:]]*$//')
 	if [ "$OUTPUT" != "${pos_cmds_out[$cnt]}" ]; then
 		log_note "Got     :$OUTPUT"
 		log_note "Expected:${pos_cmds_out[$cnt]}"