Fix Grub configurations for Fedora images built on a UEFI host.

The grub install scripts on Fedora have hardcoded checks for
/sys/firmware/efi and if the directory exists, it uses efi
specific instruction like initrdefi, linuxefi etc. vm element
should fix it once the configuration is generated.

Closes-bug: #1231946
Change-Id: I888304cb9167b8e074b04ca6c5b2f9143b70d37d
Merge "Fix Grub configurations for Fedora images built on a UEFI host."