identify output variables
BUGFIX passed an array instead of a reference
rename SetupStorage::Parted testcase directory
make Linux::LVM testable
(parse the provided data instead of actual command output)

example for 'get_volume_group_information()'

  use Linux::LVM;

  $Linux::LVM::is_testmode = 1;
  @Linux::LVM::output_vgdisplay = <sample input>;

  my %vg_info = get_volume_group_information(<vg>);
extract vgdisplay parsing logic from FAI::get_current_lvm() into a separate module
(preparation for refactoring)