Modifications for android permissions

This is inspired by
http://stackoverflow.com/questions/14149801/modify-libusb-to-accept-file-descriptor

Android USB api asks user for permission to access USB device and
on acquiring the permission, the USB fd can be obtained. This is
utilized here in making a libusb device using the same file descriptor.
libusb_open_fd should be utilised on android.

Signed-off-by: Venkatesh Shukla <venkatesh.shukla.eee11@iitbhu.ac.in>