add default user to 'sudo' group.

Ubuntu images in 12.04 added the user to the 'admin' group.
The admin group was deprecated/replaced with the 'sudo' group in 12.10.

d-i adds its first-user to the 'sudo' group, so it makes sense to mimic
that behavior for the default user created by cloud-init.  That was the
original reason behind the presense in the 'admin' group.

Also, here I sorted alphabetically the group list.

ChangeLog

@@ -23,6 +23,8 @@
    filesystems.  Useful if attached disks are not formatted (LP: #1218506)
  - Fix usage of libselinux-python when selinux is disabled. [Garrett Holmstrom]
  - multi_log: only write to /dev/console if it exists [Garrett Holmstrom]
+ - config/cloud.cfg: add 'sudo' to list groups for the default user 
+   (LP: #1228228)
 0.7.2:
  - add a debian watch file
  - add 'sudo' entry to ubuntu's default user (LP: #1080717)

config/cloud.cfg

@@ -84,7 +84,7 @@ system_info:
      name: ubuntu
      lock_passwd: True
      gecos: Ubuntu
-     groups: [adm, audio, cdrom, dialout, floppy, video, plugdev, dip, netdev]
+     groups: [adm, audio, cdrom, dialout, dip, floppy, netdev, plugdev, sudo, video]
      sudo: ["ALL=(ALL) NOPASSWD:ALL"]
      shell: /bin/bash
    # Other config here will be given to the distro class and/or path classes