make the starting apt-get update skippable/optional if starting console

[sdaau]

Thanks for the great software!

I'm trying ubuntu-builder, and since I have had great difficulties fixing the booting process, I often:

* Open console
* Make changes into grub
* Close console
* Click build, wait
* Run the .iso in VM
* Observe falure
* Open console again to make changes

At this point, it does `apt-get update` AGAIN, downloading all 15 or so MB AGAIN in however minutes it takes.... Every. time. It is **extremely** irritating.

I have already downloaded min. 200 MB from Canonical for nothing - just because of this.

I'd suggest that clicking on Console does NOT run `apt-get update` - I can always run it in a terminal if I want to. Possibly, Shift+Click on Console could run the apt-get update if needed.

Thanks!