building v19.x apps that include mysql fail because MySQLTuner download failing (in common `mysql` conf script)

[JedMeister]

As initially noted by @UncleDan on the forums and further debugged by @OnGle - the common mysql conf script is failing.

The primary issues are:

• some of the files to be downloaded no longer exist in the repo (upstream bug).
• the "raw" GH download URL is wrong.

However a curl download failure (when the default TKLDev "SSL-bump" squid proxy is used) is also a problem - see #2083