Update gradle wrapper to 1.11

Release notes for intervening versions:

http://www.gradle.org/docs/1.9/release-notes
http://www.gradle.org/docs/1.10/release-notes
http://www.gradle.org/docs/1.11/release-notes

Also added the 'project-report' plugin, which can generate a nice HTML
dependency report (added in 1.9).

  $ ./gradlew htmlDependencyReport
  $ open dist/reports/project/dependencies/index.html

Reviewed at https://reviews.apache.org/r/18294/
Fix minor issues with the tutorial

* Tutorial nicely provides URL for scheduler, unfortunately it is pointing at the wrong host.
* Correct python executable name

Reviewed at https://reviews.apache.org/r/18306/