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