Provide consistent interface to exception handlers (#3161)

This commit ensures that exception handlers are always provided with two objects:

* The Exception
* A hash with the following keys:
  * `:context` (Required) - A String message explaining what happened
  * `:job` (Optional) - If this occurred while a job was being processed, this is the deserialized job Hash
  * `:jobstr` (Optional) - If this occurred during job deserialization, this is the raw JSON string of the job
  * `:event` (Optional) - If this occurred during a lifecycle event, name of the event

lib/sidekiq/processor.rb

@@ -143,7 +143,7 @@ module Sidekiq
           # we didn't properly finish it.
           ack = false
         rescue Exception => ex
-          handle_exception(ex, job || { :job => jobstr })
+          handle_exception(ex, { :context => "Job raised exception", :job => job, :jobstr => jobstr })
           raise
         ensure
           work.acknowledge if ack

lib/sidekiq/util.rb

@@ -53,7 +53,7 @@ module Sidekiq
         begin
           block.call
         rescue => ex
-          handle_exception(ex, { event: event })
+          handle_exception(ex, { context: "Exception during Sidekiq lifecycle event.", event: event })
         end
       end
       arr.clear