add a class for android

This class use busybox for all the commandline tools.
The Android Open Source Project use 'toolbox' for the shell (implemented from scratch by Google).
However toolbox is very limited. Busybox is easily installable on Android and provide a set of tools
much more closer to the standard tools found on the other Unixes.
Merge pull request #1407 from CedricCabessa/android

add a class for android