[Android] Add driver script for running tests in emulator when cross-compiling

[weliveindetail]

When building for the host, ctest is a fast and straightforward test driver. When cross-compiling and running in an emulator like the one for Android, it causes some issues though:

• We need a different ctest binary for each target arch (and build it from source in many cases)
• The config file CTestTestfile.cmake uses absolute paths from the host machine to refer to the executables
• We still have to travers all executables and chmod +x them in the emulator manually

Given that the task of ctest is simple here, it seems reasonable to provide a script for that. With CMake filling in the test targets at configuration time, we can simply push the binary directory to the emulator and run the script in order to execute all tests.