koji: use nvra as the filename for images

We have the same thing for AWS. The AWS target also specifies under what name
should be the image available in EC2.

As requested by Brew maintainers Tomáš Kopeček and Lubomír Sedlář.

cmd/osbuild-worker/main.go

@@ -231,7 +231,7 @@ func RunJob(job worker.Job, store string, kojiServers map[string]koji.GSSAPICred
 				continue
 			}
 
-			hash, filesize, err := k.Upload(f, options.UploadDirectory, options.Filename)
+			hash, filesize, err := k.Upload(f, options.UploadDirectory, options.KojiFilename)
 			if err != nil {
 				r = append(r, err)
 				continue
@@ -274,7 +274,7 @@ func RunJob(job worker.Job, store string, kojiServers map[string]koji.GSSAPICred
 			output := []koji.Image{
 				{
 					BuildRootID:  1,
-					Filename:     options.Filename,
+					Filename:     options.KojiFilename,
 					FileSize:     uint64(filesize),
 					Arch:         common.CurrentArch(),
 					ChecksumType: "md5",