[Packaging] Use `unbuffer` when running sbuild
[Packaging] Use `unbuffer` when running sbuild

Usually when building on Jenkins, sbuild detects that there is no
tty connected, so it writes its output only to the log file. This
makes it impossible to see what's going on by looking at the
Jenkins build log. This change uses `unbuffer` to run sbuild which
causes the output to appear in the build log.

Change-Id: I0f75c3519f42772fefac0461fa0949cdc7c190cb

sillsdev/ci-builder-scripts,sillsdev/ci-builder-scripts,sillsdev/ci-builder-scripts