Make size_is_minsize usable from lvm::logical_volume

[AndreasPfaffeneder]

Currently lvm::logical_volume can not be invoked with the parameter size_is_minsize. This pr makes it configureable:

node 'default' {
  lvm::logical_volume {'test2':
    volume_group   => "vgd_${hostname}",
    size           =>'1M',
    mountpath => '/mnt/test2',
    pass => 2,
    dump => 1,
    size_is_minsize => 'true',
  }
}