Move embedded ansible worker thread up to start_runner

[jrafanie]

This is a followup to feedback in #14053 and was implemented with @carbonin's and @Fryguy 's extensive help:

• move the thread creation and knowledge to start_runner, the same place miq_worker.rb uses fork
• with thread knowledge out of the runner, we can remove our simplified do_work_loop and just use the base class's version
• remove do_exit overriding by using the long forgotten before_exit hook (at least forgotten by me)
• simplify do_work by overriding heartbeat to only call super if it's alive

[miq-bot]

Checked commits jrafanie/manageiq@18ffca9~...bba7fbf with ruby 2.2.6, rubocop 0.47.1, and haml-lint 0.20.0
3 files checked, 0 offenses detected
Everything looks good. 👍

[jrafanie]

@carbonin graciously tested this branch 🙇 and it looked good for him.

@Fryguy @gtanzillo I believe this is ready for final review/merge

[carbonin]

In my tests on a VM running in workstation with 6GB of RAM and no other workers running the initial configuration took about 7 minutes and the subsequent starts took about 1 minute.

I'm okay with this value, but we could probably make it smaller if we have a good reason to.
Thoughts?

[jrafanie]

Yeah, I don't know. As long as this timeout is used for the initial setup, a task that has a variable number of things it does, I'd be concerned with having ansible workers that can never start. I'd rather be cautious here.

[Fryguy]

LGTM, but I was partially involved. @gtanzillo Please merge if you are good with this.