Backport Gitian changes to get it to work with OpenSSH >= 7.0
jbish gave us a heads up that we need to backport some Gitian patches to keep our build environment working on Ubuntu Xenial and Debian Sid/Testing (at least) which ship OpenSSH > 7.0. He pointed us to
https://github.com/devrandom/gitian-builder/pull/107 https://github.com/devrandom/gitian-builder/pull/109