Recording "Clock Frequency" for a site leads to frequent "System Update" events

[tamiko]

CDash stores the "Clock Frequency" of the processor of a testing site.

This has the side effect that whenever the "Clock Frequency" changes a "System Update" event is recorded on the CDash page for the testing site.

With modern frequency governors (at least on Linux) this happens frequently. So with every test submission a new "System Update" is triggered on the site page.

With multiple test submissions per day this gets out of hand quickly: https://cdash.dealii.org/sites/3