Function create_fvm_volume 

pub async fn create_fvm_volume(
    volume_manager: &VolumeManagerProxy,
    name: &str,
    type_guid: &Guid,
    instance_guid: &Guid,
    volume_size: Option<u64>,
    flags: u32,
) -> Result<()>

Creates an FVM volume in volume_manager.

If volume_size is not provided then the volume will start with 1 slice. If volume_size is provided then the volume will start with the minimum number of slices required to have volume_size bytes.

wait_for_block_device_devfs can be used to find the volume after its created.