We have a "skipfuelmenu" variable in virtualbox scripts, which allows to
skip "fuelmenu" step during the installation procedure. This option is
enabled by default.
Currently, we have a hardcoded variable $boot_line, which contains scan
codes, passed by VirtualBox into isolinux on an emulated keyboard.
We should generate these scancodes from a user specified line instead of
hardcoding them.
Partial-Bug: 1525967
Change-Id: Ia2419b5e2eaa4b30cd2876112d7c080abbebcba5