[flashboot] New script for building OpenBSD installation image from install iso

[Johan Ryberg]

Hi.

I just added a new script to build image from OpenBSD install49.iso to
make a bootable USB installation pen drive.

The script is called build-usbinstallimage.sh

If any one could test the script I would be very happy. I have tested
it with both i386 and amd64 and it's possible to boot and install from
a usb stick. No more need to burn cd just for installations =)

There is how ever some kind of problem with OpenBSD own installation
script because it can't find the path to the files automatic since its
not from a CD. The path mounts upon question and the installation
proceeds without any problem.

Best regards Johan Ryberg