dc7318b8ee
46f8488a78 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