adb: don't close sockets before hitting EOF.

The standard (RFC 1122 - 4.2.2.13) says that if we call close on a
socket while we have pending data, a TCP RST should be sent to the
other end to notify it that we didn't read all of its data. However,
this can result in data that we've succesfully written out to be dropped
on the other end. To avoid this, instead of immediately closing a
socket, call shutdown on it instead, and then read from the file
descriptor until we hit EOF or an error before closing.

Bug: http://b/74616284
Test: ./test_adb.py
Test: ./test_device.py
Change-Id: I36f72bd14965821dc23de82774b0806b2db24f13