compiletest: Run all android tests serially

This is an attempt to isolate test failures on the bots. It may also
eliminate problems with the emulators breaking by reducing the chance
of OOM.
Stop looping on error waiting for android test results

These seem to be causing iloops on the bots. Let's rather see the errors.
auto merge of #12256 : brson/rust/android, r=alexcrichton

Android bot has been having some problems. A few details in the commits.