x/mobile: use java:openjdk docker base image

[proppy]

What do you think of using the official openjdk image as the base for the docker image instead of ubuntu?

Is there a specific reason you default on installing the oracle JDK?

Just tested that android 21 + openjdk seems to be able to build .apk just fine, see:
https://gist.github.com/proppy/e41195a41bea12e8c205

[hyangah]

I guess oracle jdk was chosen just because it's in the system requirement page of the android developer site https://developer.android.com/sdk/index.html#Requirements

The current way of building go mobile apps using docker image will be obsolete soon when @crawshaw 's gomobile tool becomes ready. #9508.

https://docs.google.com/document/d/1cePOQ35PNEb_QqxnPAmBv0cEnAm7AQSGuz9wVeJ-lBs/edit?disco=AAAAAT-St2U

[gopherbot]

CL https://golang.org/cl/12126 mentions this issue.