[AppStream Runner] Reduce verbosity of log output
Summary:
Its rather pointless to spew an error message each time a query is done.
Output the warning message just once (on the default logging level), and
output further messages only at debug level.
Reviewers: Plasma, ngraham, davidedmundson
Reviewed By: Plasma, davidedmundson
Subscribers: apol, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D14806