common: Print debug info when fetching summaries
common: Print debug info when fetching summaries

Sometimes fetching a remote repository's summary file fails and it can
be hard to tell what went wrong because even with --verbose flatpak
doesn't tell you which remote it's fetching from. Add a debug statement
to fix that.

Closes: #1165
Approved by: alexlarsson

handsome-feng/flatpak,handsome-feng/flatpak,flatpak/flatpak,matthiasclasen/flatpak,flatpak/flatpak,matthiasclasen/flatpak,handsome-feng/flatpak,flatpak/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,flatpak/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,handsome-feng/flatpak,flatpak/flatpak