Bump SSHD version to 0.10.1 and enable nio2 backend

46f8488a78742799a4f5f781279c8955460e7964 removed nio2 backend because of
a bug [1].  Given that the bug is fixed and released, enable it again.

Another problem was also fixed and released [2].

Upgrade to the official version 0.10.1 makes Gerrit's own custom patch of
SSHD and hosting it on Google bucket unnecessary.

[1] https://issues.apache.org/jira/browse/SSHD-252
[2] https://issues.apache.org/jira/browse/SSHD-255

Bug: Issue 2406
Change-Id: I6668f6194427f153e1982e14b3936d2f3132fa7d
Update sshd to 0.11.0

Fixes a few issues including a null pointer exception [1] that causes
ssh commands to hang.

It also adds server driven rekeying after 1G bytes of data transferred,
which is a useful security feature.

[1] https://issues.apache.org/jira/browse/SSHD-307

Change-Id: I441995eaf76e4fe53f7991f5aef00e062900791b
Merge changes I441995ea,I6668f619 into stable-2.8

* changes:
  Update sshd to 0.11.0
  Bump SSHD version to 0.10.1 and enable nio2 backend