Add accessorytest Linux host tool for testing USB accessory audio and HID support.

The tool supports testing USB audio by default.
It reads audio from the ALSA device for the android phone in accessory mode
and outputs it to the ALSA device for the PC's speaker.
The default values work on my PC, but can be changed via command line options.

When the -a option is specified, accessorytest also acts as the host side of the
AccessoryChat test, so audio can be tested side by side with the accessory bulk endpoint support.

When the -h option is specified, accessorytest will look for HID devices on the PC and proxy them
to the phone over the accessory protocol. This requires running accessorytest as root.

Change-Id: I1ea06d7201cd845b95a92a42594464783a90189b