ST-1322: Trogdor Produce Runner

[yangxi]

The Trogdor Runner executes Trogdor ExternalCommandSpec tasks. It can be invoked directly from command line ./tests/trogdor_runner --spec ExternalCommandSpecFile, or driven by Trogdor agents. When running from command, the Trogdor Runner reads the spec file. If driven by Trogdor agents, this runner is waiting on the stdin for the ExternalCommandSpec tasks, then execute the tasks.

• Add Trogdor Runner (./tests/trogdor/trogdor_runner.py) to execute Trogdor tasks.
• Add Trogdor Produce Runner (./tests/trogdor/produce_spec_runner.py) to execute Trogdor Produce task.
• Add Trogdor Produce Test to ./tests/run.sh.

[yangxi]

@edenhill Thanks for the review. I addressed most of your comments.

[mhowlett]

I'm going to progress the work in this PR over here: https://github.com/mhowlett/confluent-kafka-python/tree/trogdor

I'll add to the comments in this PR, where relevant, but make updates to my own branch. we can sort out anything already raised in comments here, and continue the discussion in my branch when done.

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