adb unittest for win32 handle inheritance

adb.cpp: launch_server() has a long comment about how
stdin/stdout/stderr handles have to be made non-inheritable to prevent
hangs in callers to adb.exe.

It would be disastrous to do this wrong, and I've modified this code, so
here's a unittest to verify that I'm doing it right.

The test also runs fine on unix.

Change-Id: I3672c3066bc7498635c19212f9e5c50757942439
Signed-off-by: Spencer Low <CompareAndSwap@gmail.com>