Climb cause chain to determine if exception is due to Sidekiq::Shutdown.
Improve code style for exception_caused_by_shutdown?
Test handling exceptions during Sidekiq::Shutdown.
Mark tests that cannot pass under Ruby < 2.1.0 as pending on those versions.
Merge pull request #1813 from avalancheau/fix-activerecord-retry-on-restart

Improved (and more effective) fix for catching and ignoring exceptions caused by Sidekiq::Shutdown