Add initial HDFS tests

[yongtang]

This PR adds initial HDFS tests. The HDFS server is setup with sequenceiq/hadoop-docker:2.7.0 to start with.

This is part of #1183.

Signed-off-by: Yong Tang yong.tang.github@outlook.com

[vnghia]

Hi @yongtang

I have some questions:

• Should we merge the tests here after add test for filesystem plugins #1221 is done ? I have to put add test for filesystem plugins #1221 on hold because of New filesystem plugins throw segfault #1222. I am investigating but it will take sometime cause building pip package for TensorFlow took me a lot of time. ( I am suspecting that memset and memcpy does not preserve the nullptr. )

• Regarding GCS test, I am thinking of copying the emulator from google-cloud-cpp to this repository. Or I could create a Docker image for it. Which one do you prefer ?

[yongtang]

@vnvo2409

Should we merge the tests here after #1221 is done

I think we can merge this PR first for now. This PR setup the Hadoop with docker image sequenceiq/hadoop-docker:2.7.0. Though the test that has been added in this PR is really bare-bone. It just shows that Hadoop setup is working. The added test can be easily migrated to the parameterized pytest you have been doing after #1221 is done.

Regarding GCS test, I am thinking of copying the emulator from google-cloud-cpp to this repository. Or I could create a Docker image for it.

I think copying the emulator from google-cloud-cpp is good enough 👍

[vnghia]

I think we can merge this PR first for now

Ah sorry, I mean merge the tests in this PR to #1221 😄

[kvignesh1420]

LGTM.