Only delete files in group when doing full file backup
Only delete files in group when doing full file backup

(cherry picked from commit b48426665dbc542fc780c1964c770d32510858e9)

uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend