Some UEFI firmwares may want to use a non-volatile memory to store
variables.
This requires to specify loader and nvram to use UEFI boot in QEMU.
Specifying loader and nvram at the same time will set loader to
type 'pflash' instead of 'rom'.
If loader is used without nvram option type will remain 'rom'.
Further information can be found at libvirt documentation:
https://libvirt.org/formatdomain.html#elementsOS
This commit lets users enable hostname randomization from their
Vagrantfile. Without this option enabled, domain creation will fail when
multiple VMs are spun up from the same Vagrantfile, due to a domain name
conflict.
