Upgrade gradle to 2.9

Summary:
public

New version of gradle has a better support for zipTree copy task. Since we have a few of those including one for boost library which used to take very long, after upgrading we no longer need 6a656a1.

Also seems like many improvements made to gradle since 2.2 made it perform better on incremental builds (around 10% improvement on my laptop).

Command used to upgrade gradle version:

    gradle wrapper --gradle-version 2.9

Some of the plugins require updating as well since the previous versions were incompatible with gradle 2.9.

Closes https://github.com/facebook/react-native/pull/4462

Reviewed By: mkonicek

Differential Revision: D2754786

Pulled By: mkonicek

fb-gh-sync-id: 92c07d29aec6d5b4b2c55205b42b135c4d9479a9