misc/android: serialize adb commands on android emulators
Android emulator builders are soon to join the trybot set. To avoid
flaky runs, work around a longstanding adb bug where concurrent adb
commands sometimes fail.
I haven't seen the problem on actual devices until recently. It seems
that the recently added "adb wait-for-device" can introduce flakyness
with errors such as:
adb: error: failed to get feature set: protocol fault (couldn't read status): Connection reset by peer
Instead of working around that, give up and serialize use of adb
everywhere.