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ARROW-6466: [Integration][CI] Move integration test code to `archery integration` command. Dockerize integration tests

This makes the integration tests part of the archery CLI tool. Note that this also drops Python 2.7 support for these tests. I think given that it's October 2019 that's okay.

The integration tests are now run with `docker-compose run integration`

Closes #5600 from wesm/integration-to-archery and squashes the following commits:

7c0ee6f6f <Wes McKinney> Restore debug flag. Install NumPy
1a09f1693 <Wes McKinney> Port integration tests to archery

Authored-by: Wes McKinney <wesm+git@apache.org>
Signed-off-by: François Saint-Jacques <fsaintjacques@gmail.com>