Move logging, updating and testing utils into common directory

This is part of a series of PRs which add up to a substantive change.

I used '.' in import statements in some places to bring the symbols into the current namespace, to reduce the quantity of diffs in this patch.  I can do it the other way if preferred.
> (a) I'm not super-happy about dotted import in general

I am fine with them. In fact one criteria for whether something should go into `common` could well be whether it makes sense to have it dotted-imported.

> (b) it didn't make any difference in this file to the overall number of diffs

Yes, but all other code imports `common` dotted, and hence accesses the logging vars unqualified.