Use middlewared for manual execution of cron job tasks

When running a cron job manually (via GUI: Tasks-->Cron-->'Run Now' option on task), reports of stdout/stderr are not emailed to user. Emails ARE sent when cron runs them according to schedule.

review thread: https://www.ixsystems.com/community/threads/is-there-a-better-way-to-poll-my-ups-for-self-test-status.75854/

tldr: created python script to run UPS self-tests, script prints result (pass/fail) to stderr on exit to report status to user. stderr report not sent when running manually via GUI, but DID receive an email when script was run per its schedule.