Fix OpenCVConfig.cmake generated for Android platform (issue #2496)

* fix path to libraries in Android SDK
* allow to link to opencv_java.so as Android.mk does

To link to opencv_java.so you can either change your cmake to find OpenCV as

    find_package(OpenCV opencv_java)

or pass -DOpenCV_FIND_COMPONENTS=opencv_java to your cmake command
Merge pull request #570 from taka-no-me:fix_android_cmakeconfig