adb: add `adb shell exit 42` stress test.

Add a test to hammer on `adb shell exit $n` for flakiness.

Bug: http://b/74616284
Test: python test_device.py
Change-Id: I6a842960f5b55ff739044698f5c9683992fc42f1
(cherry picked from commit 160bf7ece8e499e6f31ada1b04dec5a7e40395b6)
1 file changed