pass context to Find / FindSnapshot

This allows proper interruption of restic while it searches for
snapshots or key files.

cmd/restic/cmd_dump.go

@@ -160,7 +160,7 @@ func runDump(opts DumpOptions, gopts GlobalOptions, args []string) error {
 			Exitf(1, "latest snapshot for criteria not found: %v Paths:%v Hosts:%v", err, opts.Paths, opts.Hosts)
 		}
 	} else {
-		id, err = restic.FindSnapshot(repo, snapshotIDString)
+		id, err = restic.FindSnapshot(ctx, repo, snapshotIDString)
 		if err != nil {
 			Exitf(1, "invalid id %q: %v", snapshotIDString, err)
 		}