test_vendor_lib: Initial commit

Basic vendor library for a test Bluetooth controller. Currently consists
of mostly stub functions and objects and can only handle the reset
command (by immediately responding with a command complete event).
Implemented through a global EventDispatcher object which waits for data
from the HCI and directly returns the appropriate response.

Eventually, the dispatcher will manage a fake controller object that
will provide callbacks to be executed whenever events are processed by
the dispatcher. Unit tests are still in progress and will be in the next
upload.

Bug: 21586676
Change-Id: I1c6746f8b0f1732b89a1da13facecdd49b5ac1b6