Skip restart if deploy script reports no code changes

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essentially:

• The deploy stage can now return a dictionary of

  "component@hash": true/false,
  ....
  }

  Determining whether or not that component is safe to skip a restart for.

• If all components have the false bit set, we skip the remaining commands for that host, which will be the restart and wait-for-components commands.

I did a little bit of refactoring for this to avoid dumping more conditional logic into deploy.py --

• I replaced the use of ["command", "args"...] lists with command objects where deploy lifecycle logic can be defined. I'm not super married to this refactor as it doesn't really buy too much right now, but the pattern seems to feel to feel a bit better now that we're starting to add more conditional logic to the deploy flow.
• generalized the mock transport a bit so different behavior can be mocked out.

[eaceaser]

:eyeglasses: @spladug @alienth

[alienth]

:running: feel free to re-summon when this is active again.

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:haircut_woman:

PR necromancer! this is back from the dead.

Since the last PR:

• I fixed up the review comments.
• I realized that the deploy short-circuiting will also short-circuit any explicit commands you define on the commandline. Specifically if you explicitly say to restart hosts, or if you execute a custom command. This is a bit non-obvious behavior.

The workaround is to set a boolean on the command to flag if it was explicitly added or not. Currently I'm doing this for custom commands and restart commands. Then, the restart short-circuiting will only filter out commands that were not explicitly added.

I'll refresh the puppet PR separately. I tested this on gangplank, but I still need to do a r2 and mothership test, but I wanted to get this out in front of eyeballs.