Add final execution hooks to luigi, as well as batched counter increments

Change-Id: I6aba342a446a8b039ac6fcd7379cfce9f859f659
Reviewed-on: https://gerrit.spotify.net/gerrit/43537
TC-Compile-And-Test: Team City <teamcity@spotify.com>
Reviewed-by: Elias Freider <freider@spotify.com>

Conflicts:
	.gitignore
	luigi/hadoop.py