arrow

ARROW-3368: [Integration/CI/Python] Add dask integration test to docker-compose setup

Port dask integration testing, and refactored the hdfs one.
Multiple python hdfs tests cases are failing, nut sure why.

Author: Krisztián Szűcs <szucs.krisztian@gmail.com>

Closes #3086 from kszucs/ARROW-3368 and squashes the following commits:

d6e98ecb8 <Krisztián Szűcs> resolve load warning of native-hadoop library
237440ab0 <Krisztián Szűcs> cleanup
0b3e1fc4c <Krisztián Szűcs> port fastparquet hdfs test
c497be0d6 <Krisztián Szűcs> better error msg
cf06721ef <Krisztián Szűcs> minimal hdfs config
d1e9b3717 <Krisztián Szűcs> arrow- test executable prefix
5c11d72ed <Krisztián Szűcs> add hdfs config files
f7681d045 <Krisztián Szűcs> download hadoop from apache mirrors
c84294a56 <Krisztián Szűcs> update comment
1eef5bfa8 <Krisztián Szűcs> remove dask_integration.sh
00ef67691 <Krisztián Szűcs> two datanodes; support env vars in conftest
c2bc444c2 <Krisztián Szűcs>  remove outdated files
840f313b3 <Krisztián Szűcs>  test optional modules
0e8b3932b <Krisztián Szűcs>  add dask-integration to nightlies
c3d4a9bef <Krisztián Szűcs> remove comments from docker-compose
ffe0ac7ea <Krisztián Szűcs> set hadoop version to 2.6.0
1c7bf304d <Krisztián Szűcs> unset LD_LIBRARY_PATH
f1af0248d <Krisztián Szűcs> run dask tests
694e7e6ef <Krisztián Szűcs> docker-compose setup for dask integration