Read stderr from server for a short time before exiting

Previously we exited immediately without waiting to get any
error output.

This patch also adds the command line and directory to the
exception message on failure, in case the failure is due to
getting one of those wrong, for example.
ServerApplication: yield before we check on the dumper thread
put backticks around `yield` in Thread.yield
Merge pull request #1377 from havocp/wip/havocp-server-launch-errors

Read stderr from server for a short time before exiting