qubes/backup: py3k related fixes
qubes/backup: py3k related fixes

- str/bytes usage
- functools.reduce
- dict.items instead of dict.iteritems etc

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