Currently we only shut down on EIO. Expand this to shut down on any
system_error.
This may cause us to shut down prematurely due to a transient error,
but this is better than not shutting down due to a permanent error
(such as ENOSPC or EPERM). We may whitelist certain errors in the future
to improve the behavior.
Fixes#1311.
Message-Id: <1465136956-1352-1-git-send-email-avi@scylladb.com>