Fix false busy detection of unusual case with Linux Software RAID (#712533)

In this unusual setup of having one Linux Software RAID array
partitioned and a second array not partitioned, /dev/md1p1 partition in
the first array is falsely reported as busy when the file system filling
the second array /dev/md2 is mounted.

  Partition   RAID                File System        Mount mount
  ---------   -----------------   ----------------   -----------
  /dev/sdb1   SWRAID /dev/md1
                     /dev/md1p1   ext4,Label=test1   (Unmounted)
  /dev/sdb2   SWRAID /dev/md2     ext4,Label=test2   /mnt/2

This again affects Debian 6, Debian 7 and RHEL/CentOS 6.x and is as a
result of the this bug fixed in libparted 2.4:
    http://git.savannah.gnu.org/cgit/parted.git/commit/?id=db52898c214310dab4ed84e6cb2f9ffc8c3aa502
    linux: also detect "in-use" dmraid and scsi-Nth (N>=16) partition

Fix by not using libparted's ped_partition_is_busy() to determine if a
normal or logical partition is busy.

Bug #712533 - Partitions not detected as busy inside Software RAID on
              some distros