Re-enable previously disabled test

Seems like I accidentally committed this completely disabled.
Make TestErrorDuringStartup more resilient against different setups

While the previous coding would always work in Travis, there's no reason
to fail "go test" on other setups.
Change the type of saveMessageBuffer

It makes more sense to store it as a byte slice since that's how we
ultimately treat it.
Mark the connection bad in a couple of more cases
Mark the connection bad on unexpected panics

Since we have no way of knowing where things went wrong, consider the
connection bad in its entirety.