ledflasher: Implement base.identify and pairing session confirmation

Added a handler for base.identify command that would flash LEDs on the
board for 2 seconds. Also when the device goes into pairing mode, its
LEDs will flash as well to confirm that the client is connected to the
right physical device.

BUG: 26467076
Change-Id: I7ef31e9d2694c46b6d9c61b209f3e50b99fc3258