Merge pull request #1825 from arges/ubuntu

Changes to update Ubuntu cfg, ini, and preseed files.
virttest: add help flags for QemuImg help_text

When calling qemu-img with no arguments in qemu 2.1 the following is printed:
qemu-img: Not enough arguments

This adds the --help flag to ensure that 'qemu-img check' works.

Signed-off-by: Chris J Arges <chris.j.arges@canonical.com>
guest-os: update single_user_cmd to work with Ubuntu guests

The tests 'reboot_time' and 'boot_time' fail on Ubuntu unless single_user_cmd
is updated with this command.

Signed-off-by: Chris J Arges <chris.j.arges@canonical.com>