gs-shell: Change which errors are ignored for refresh and update non-interactive actions
Background refresh/update can fail with various errors, some might be important to the user
even for non-interactive updates, thus make such errors are shown in the GUI.
gs-dbus-helper: Make sure non-NULL values are used for GVariant
It can happen some of the values passed to the install_resources()
are NULL, but passing such into g_variant_new_string() causes
a runtime warning, because the function does not accept NULL strings.
gs-vendor: Ignore ENOENT for /etc/PackageKit/Vendor.conf file
The Vendor.conf might not exists on system without PackageKit, though
the sources can be compiled with the PackageKit support, thus instead
of claiming the file does not exists on every start of the gnome-software,
claim an error only if the file exists and it fails to read data from it.