android_pipe: Factor out example/test pipes from android_pipe

The Android Pipe main implementation file should only contain the actual
implementation.  Keeping all that test backend implementation code in
there just makes it confusing to grep in the file and figure out what is
going on.

This could be made dependent on some sort of debug flag to avoid
compiling test code as part of shipped binaries in the future.

Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>