When a task outputs data that cannot be serialized to JSON the task will stacktrace

[donoghuc]

Describe the Bug

When a task result cannot be serialized to JSON in

bolt/lib/bolt/result.rb

Lines 141 to 143 in 6851fc8

	def to_json(opts = nil)
	status_hash.to_json(opts)
	end

there is a stacktrace:

cas@cas-ThinkPad-T460p:~/working_dir/bolt/Boltdir/site/test/tasks$ bolt task run test::big -t localhost
Started on localhost...
<JSON::GeneratorError> source sequence is illegal/malformed utf-8
	/home/cas/working_dir/bolt/lib/bolt/result.rb:142:in `to_json'
	/home/cas/working_dir/bolt/lib/bolt/result.rb:142:in `to_json'
	/home/cas/working_dir/bolt/lib/bolt/executor.rb:237:in `with_node_logging'
	/home/cas/working_dir/bolt/lib/bolt/executor.rb:274:in `block (2 levels) in run_task'
	/home/cas/working_dir/bolt/lib/bolt/executor.rb:115:in `block (3 levels) in queue_execute'
	/home/cas/working_dir/bolt/vendor/bundle/ruby/2.5.0/gems/concurrent-ruby-1.1.6/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:353:in `run_task'
	/home/cas/working_dir/bolt/vendor/bundle/ruby/2.5.0/gems/concurrent-ruby-1.1.6/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:342:in `block (3 levels) in create_worker'
	/home/cas/working_dir/bolt/vendor/bundle/ruby/2.5.0/gems/concurrent-ruby-1.1.6/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:325:in `loop'
	/home/cas/working_dir/bolt/vendor/bundle/ruby/2.5.0/gems/concurrent-ruby-1.1.6/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:325:in `block (2 levels) in create_worker'
	/home/cas/working_dir/bolt/vendor/bundle/ruby/2.5.0/gems/concurrent-ruby-1.1.6/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:324:in `catch'
	/home/cas/working_dir/bolt/vendor/bundle/ruby/2.5.0/gems/concurrent-ruby-1.1.6/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:324:in `block in create_worker'
	/home/cas/working_dir/bolt/vendor/bundle/ruby/2.5.0/gems/logging-2.2.2/lib/logging/diagnostic_context.rb:474:in `block in create_with_logging_context'
Finished on localhost:
Failed on 1 target: localhost
Ran on 1 target in 0.11 sec

It looks like the task spec suggests handling this specific case with a special error https://github.com/puppetlabs/puppet-specifications/tree/master/tasks#errors

Expected Behavior

Better description of error than a JSON serialization stack trace.