Bug 27820: add all missing use in misc/cronjobs/plugins_nightly.pl

Bug 27820: add all missing use in misc/cronjobs/plugins_nightly.pl

Koha::Plugins and C4::Context where missing.
Try::Tiny was missing for try/catch.

Test plan :
1) Use a plugin using hook 'cronjob_nightly'
2) Run script : misc/cronjobs/plugins_nightly.pl

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 5a2dfc5ea36d45d7af9c0e4102f92a601e192b46)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>