adding copy command

Change-Id: I0898a0e273d5e567a2fd947731200788f451484f
Reviewed-on: https://gerrit.spotify.net/gerrit/46993
TC-Compile-And-Test: Team City <teamcity@spotify.com>
Reviewed-by: Elias Freider <freider@spotify.com>

Conflicts:
	luigi/hdfs.py
Use LocalJobRunner for MapReduce if there are non-HdfsTarget outputs

Change-Id: Ie406af4a5e479dc4bb7ff8c6ecb8469713b3fe99
Reviewed-on: https://gerrit.spotify.net/gerrit/44957
Reviewed-by: Elias Freider <freider@spotify.com>
Renamed _repr_reader/writer and created an alternative reader/writer using pickle

Change-Id: If3c1873dad874bf3c7f3f50ea1dff9dd47dbaf8d
Reviewed-on: https://gerrit.spotify.net/gerrit/47106
Reviewed-by: Erik Bernhardsson <erikbern@spotify.com>
Reviewed-by: David Whiting <davw@spotify.com>
Reviewed-by: Elias Freider <freider@spotify.com>