adb: add test for flushing socket data after a write failure.

Add a currently failing test that's a reduced case of the 'concurrent
adb shell' flakiness reported in b/74616284.

Bug: http://b/74616284
Test: changed #if 0 to #if 1, test fails
Change-Id: Id170a185f7c5d2ff44f772f7849a73227f9df441