[scripts] Mono has only packages for LTS versions
[scripts] Mono has only packages for LTS versions

For any non-LTS Ubuntu version we install mono from the latest LTS
version.

Change-Id: I1c31dad902daaba77bf093b991a2c8849405cbd1

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