Update the test droid image build

[troydai]

Speed up the test lising process and remove dependency of a root image.

1. Derive from python:3.6-jessie instead of base a01 droid image
2. Load job.py from this repo
3. Collect tests and generate test index file during building.

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[troydai]

@derekbekoe I can go through this change with you offline.

[promptws]

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