[RFC] Upgrade Jenkins EC2 plugin to 1.13 on Android Build

Hello,

We're running Jenkins EC2 plugin v 1.11 on android-build.linaro.org, which is 2 releases behind the latest 1.13. Per ChangeLog, it fixes slave label expression evaluation, which affected me once when I tried to do more flexible slave selection for builds (we fortunately were able to get past it by the fact that we use same 64-bit slave type for both platform and toolchain builds).

So, I'd like to schedule an upgrade some time next week, to allow for sandbox testing and feedback collection time.