backup: add qvm-backup-restore --rename-conflicting option
backup: add qvm-backup-restore --rename-conflicting option

QubesOS/qubes-issues#869

woju/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin