Make custom_key_dir a class parameter and not a global variable

Conflicts:
	manifests/init.pp
fix default unattended-upgrades config file
using distribution sprecific files again
fix unattended-upgrades dependency cycle
Updating unattended-upgrades squeeze config as oldstable (2)
Changing 'testing' to 'wheezy' on 50unattended-upgrades.wheezy
Regression: lost MailOnlyOnError for unattended-upgrades

Since only wheezy supports it, let's add it back only for wheezy.

Signed-off-by: Gabriel Filion <gabster@lelutin.ca>