Add "oldstable" to the default update origins for wheezy

Add "oldstable" to the default update origins to ensure
the updates keep working after wheezy+1 gets released

See unattended-upgrades 0.79.5+wheezy1 and https://bugs.debian.org/711826
Fix "WARNING: indentation of => is not properly aligned on line 9"
Fix "WARNING: case statement without a default case on line ..."
Merge pull request #376 from raoulbhatia/unattended-upgrades-oldstable

Unattended upgrades oldstable for wheezy