Usb-creator should use "-vga std" (or "-vga vmware") option on QEMU-KVM launch ("Test Disk") for better compatibility with modern versions of Ubuntu

[Norbert]

STEPS TO REPRODUCE:
   1. Launch usb-creator-gtk (for example from Ubuntu 12.04.5 LTS)
   2. Choose iso-image to create LiveUSB (12.04 LTS, 14.04 LTS, 14.10, 15.04)
   3. Press "Make Startup Disk"
   4. LiveUSB was created ("Installation Complete" window)
   5. Pressed "Test Disk"
   6. Got error message in QEMU window ("gfxboot.c32: not a COM32R image") - it is known bug 1325801 , enter "live" here
   7a. Boot to corrupted desktop (12.04 LTS, 14.04 LTS, 14.10 ) - it is bug 1080674
   7b. Boot to failsafe mode (15.04) - it is bug 1437740

EXPECTED RESULTS:
   usb-creator-gtk is compatible with modern versions of Ubuntu, user can boot and test new versions of Ubuntu in it.

ACTUAL RESULTS:
   usb-creator-gtk launch kvm without -vga option, guest system does not work with full graphics performance. User is disappointed.

FIX:
   Developers can choose between two solutions - fix the problem on distro-side (in QEMU-KVM guest system), or pass "-vga std" (or "-vga vmware") to kvm command on execution of "Test Disk" procedure.

NOTES:
  I prepared google docs table ( https://docs.google.com/spreadsheets/d/1WsjQ8nz3b6dhYGdM3xxkdxZHp27j9ggvrRPcZbm9Cao/edit?usp=sharing ) for better understanding the problem with screenshots.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: usb-creator-gtk 0.2.38.3ubuntu0.1
ProcVersionSignature: Ubuntu 3.13.0-49.81~precise1-generic 3.13.11-ckt17
Uname: Linux 3.13.0-49-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.0.1-0ubuntu17.8
Architecture: amd64
Date: Sun Apr 26 19:03:44 2015
InstallationMedia: Ubuntu 10.04 LTS "Lucid Lynx" - Release amd64 (20100429)
MarkForUpload: True
SourcePackage: usb-creator
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.