Use same preseed file for all Debian 7 releases

The files were and most probably always should be identical.
Add packer templates for Debian 7.4
Update Debian 7.2 and 7.3 default mirror URLs

They are now archived after Debian 7.4 release.
Fix DHCP lease directory name in Debian

Both Debian 6.0 and 7 use /var/lib/dhcp instead of dhcp3.
Use sudoers.d in Debian

Debian 6.0+ have sudoers.d enabled by default. Use it so that the
provisioners (like Chef) don't need to agree on using "sudo" group, or
know anything about "vagrant" user if it manages the /etc/sudoers file.
Use builder specific output directories also for Debian 7.3 and 7.4
BENTO-112 add single-request-reopen to resolv.conf
Merge pull request #162 from tmatilai/debian-dhcp

Fix DHCP lease directory name in Debian
Merge pull request #163 from tmatilai/debian-sudoers

Use sudoers.d in Debian
Merge pull request #165 from rjocoleman/single-request-reopen

BENTO-112 add single-request-reopen to resolv.conf
Remove old Debian 7 update releases
Rename Debian 7.4.0 to Debian 7.4

The official version is "7.4" even though the download URL uses the
extra digit.
Merge pull request #164 from tmatilai/debian-7.4

Add Packer templates for Debian 7.4