create-image.sh: disk image generation now supports grub1 based distribu...

...tion

Add grub1 support when generating virtual disk image. However we use extlinux
as installing grub1 in a chroot is not very reliable.

During the virtual disk image creation the bootloader installation process
detect whether grub2 is available or not, if not extlinux is used.

For redhat based distribution the automatic network configuration settings
is now properly handled.