[Python] Run s3fs unit tests in Travis CI

[asfimport]

We'll need to set up an S3 bucket to write to with credentials that cannot compromise anyone's AWS account. I've been testing locally with a user that I set up but I wouldn't be comfortable checking in these credentials, even in encrypted form, without more scrutiny

Reporter: Wes McKinney / @wesm
Assignee: Krisztian Szucs / @kszucs

Related issues:

• [C++] Add filesystem implementation for Amazon S3 (relates to)

PRs and other links:

• GitHub Pull Request #5423

_{Note: This issue was originally created as ARROW-1456. Please see the migration documentation for further details.}

[asfimport]

Florian Jetter / @fjetter:
Mocking s3 may already be enough for the arrow unit tests. E.g. https://github.com/spulec/moto

[asfimport]

Uwe Korn / @xhochy:
Alternatively we could setup a small S3 server in Docker using https://github.com/minio/minio

[asfimport]

Krisztian Szucs / @kszucs:
Resolved by #5423