Fix bug 697 - task-scheduler: should verify valid cron file name

Signed-off-by: Daniil Baturin <daniil@baturin.org>
Fix bug 696 - task-scheduler: restart script missing

Signed-off-by: Daniil Baturin <daniil@baturin.org>
First check is not needed, the second check is probably too limiting
as it prevents the user from executing system commands.
1.0.3+vyos1+helium7