Fix updating remotes' appstream
Submitted by Joaquim Rocha
Currently if there are multiple remotes to fetch the appstream data from, and doing so fails for one of them, then the remaining remotes will never be updated. This leads to cases where, e.g. having one remote with a broken gpg key (or with a user without permissions to pull from an untrusted source) may prevent getting updates from other valid remotes.
Maybe the solution I provide is an easy one but in any case, one failing remote should never prevent refreshing the appstream data of other remotes so I think the operation should continue and a warning should be printed when that situation happens.