adb: don't close sockets before hitting EOF.

Reimplement commit ffc11d3c using
fdevent. The previous attempt was reverted because we were blindly
continuing when revents & POLLIN == 0, which ignored POLLHUP/POLLERR,
leading to spinloops when the opposite end of the file descriptor was
shutdown when we had no data left to read.

This patch reimplements the functionality implemented by that commit
using fdevent, which gets us detection of spin loops for free.

Bug: http://b/74616284
Test: ./test_device.py
Change-Id: I1abd671fef4c29e99dad968aa66bb754ca382578