Fix increasing priority on Linux
Fix increasing priority on Linux

(cherry picked from commit 820d6fba3f973d9503eb40be6dcca33e0aded6de)

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