adb: allow selection of a specific transport.

Extend device selection to allow selecting a specific transport via
monotonically increasing identifier (visible in devices -l).

This is useful when using multiple devices (like hikey960...) that
have identical bogus serial numbers like 0123456789ABCDEF.

Bug: http://b/37043226
Test: adb -t {1, 2, 9999999} {get-serialno, shell, features}
Change-Id: I55e5dc5a406a4eeee0012e39b52e8cd232e608a6