* gnu/build/vm.scm (<partition>)[file-system-options]: New field.
(create-ext-file-system, create-fat-file-system)
(format-partition): Add #:options and honor it.
(initialize-partition): Pass #:options to 'format-partition'.
* gnu/system/vm.scm (qemu-image): Add #:file-system-options and use it
for the root partition.