Get a more detailed error message when instrumentation fails

The way this works is that when we get an error from
`adb shell am instrument`, we try to rerun the same command
with `-w` (wait for instrumentation to finish) so we get more 
details.

We don't want to always start instrumentation with `-w` because
this will timeout in the success case.

We append the `-w` right after `shell am instrument`. Appending
it to the end of command doesn't appear to be working.