Improve test failure message for #1390.
Improve error message further.
Add special hook to diagnose travis failing test.
Wait 5 seconds instead of 2 seconds to read stderr from launched server
Flush output every time we write to it in StreamDumper

To try harder to get our errors displayed.
Don't delete the server config file if SBT_SERVER_SAVE_TEMPS ne null

This allows people to reproduce failures by running the command line
by hand.

Fixes #1394
Remove flaky test.

Fixes #1390
Merge pull request #1397 from havocp/wip/havocp-try-harder-for-errors

Try harder to get diagnostics on server launch failure
Merge pull request #1391 from sbt/wip/1390

Improve test failure message for #1390.
Merge remote-tracking branch 'upstream/0.13' into 0.13