Android: Set JAVA_HOME in environment and use that environment

Change-Id: Ia0f3abad74b7ac423fab621ca22e0f698747c477
Reviewed-by: BogDan Vatra <bogdan@kde.org>
Reviewed-by: Ray Donnelly <mingw.android@gmail.com>
Android: Autodetect a value for OpenJDK path

First look into the current PATH, secondly into the registry.

Change-Id: I3b1d1ebccb1a85c03979ac3d48740c3de5a6df40
Reviewed-by: BogDan Vatra <bogdan@kde.org>
Reviewed-by: Ray Donnelly <mingw.android@gmail.com>
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Reviewed-by: Daniel Teske <daniel.teske@digia.com>