Bumping the sample gradle build tools to 1.2.0

This fixes some build flakiness: see
http://stackoverflow.com/questions/29026024/errorexecution-failed-for-task-projectnamemergedebugresources-crunching

Change-Id: I92fd6dc7abfcdca4106c54b001c8e5f232bfb446
Tested: Built all samples.
(cherry picked from commit cfd648e7aae892c2e0d65923f105041f3362529b)
7 files changed