#2988: Improve configure_gums error reporting

When configure_gums is doing the copy-configuration step, it fails to log useful
information from the mysqldump command (at least). We need to be sure that all
system commands log useful information for debugging. Also, while we're in
there, we might consider trying to provide more useful error messages.

The first step is to review configure_gums (esp. copy_configuration()) and
figure out how much work there is to do. After that, we may fiddle with the
priority of the ticket.

I've tested the changes manually. It seems to copy the old GUMS config just fine
(i.e., I didn't break it). When there are problems with the old database, it
does report better debugging messages. And nothing is broken in routine nightly
testing, which doesn't hit the copy-config stuff but at least I didn't break the
normal case.