sshd: work around a race condition in Apache MINA sshd 2.4.0/2.5.x

sshd: work around a race condition in Apache MINA sshd 2.4.0/2.5.x

When exceptions occur very early in the SSH connection setup, it's
possible that an exception gets lost. A subsequent authentication
attempt may then never be notified of the failure, and then wait
indefinitely or until its timeout expires.

This is caused by race conditions in sshd. The issue has been reported
upstream as SSHD-1050,[1] but will be fixed at the earliest in sshd
2.6.0.

[1] https://issues.apache.org/jira/projects/SSHD/issues/SSHD-1050

Bug: 565394
Change-Id: If9b62839db38f9e59a5e1137c2257039ba82de98
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>