adb: fix transport acquisition for forward, reverse.

Previously, we were calling acquire_one_transport with all empty
parameters, which would work when only one device is connected, but fail
when there are multiple. We've already acquired a transport and put it
into the socket as part of the forward request, so just use that
directly.

Bug: http://b/136198949
Test: test_device.py with multiple devices connected
Change-Id: I4d6bda45b36b71e418ecd9ead61b7379e68aa19b