Bug 1202813

Description of problem:
custom install  std format on usb ext HD with provious install

Version-Release number of selected component:
anaconda-core-22.20.4-1.fc22.x86_64

The following was filed automatically by anaconda:
anaconda 22.20.4-1 exception report
Traceback (most recent call first):
  File "/usr/lib64/python2.7/site-packages/parted/disk.py", line 215, in commit
    return self.__disk.commit()
  File "/usr/lib64/python2.7/site-packages/parted/decorators.py", line 41, in new
    ret = fn(*args, **kwds)
  File "/usr/lib/python2.7/site-packages/blivet/formats/disklabel.py", line 269, in commit
    self.partedDisk.commit()
  File "/usr/lib/python2.7/site-packages/blivet/devices/partition.py", line 670, in _destroy
    self.disk.originalFormat.commit()
  File "/usr/lib/python2.7/site-packages/blivet/devices/storage.py", line 538, in destroy
    self._destroy()
  File "/usr/lib/python2.7/site-packages/blivet/deviceaction.py", line 346, in execute
    self.device.destroy()
  File "/usr/lib/python2.7/site-packages/blivet/devicetree.py", line 361, in processActions
    action.execute(callbacks)
  File "/usr/lib/python2.7/site-packages/blivet/blivet.py", line 162, in doIt
    self.devicetree.processActions(callbacks)
  File "/usr/lib/python2.7/site-packages/blivet/osinstall.py", line 1057, in turnOnFilesystems
    storage.doIt(callbacks)
  File "/usr/lib64/python2.7/site-packages/pyanaconda/install.py", line 188, in doInstall
    turnOnFilesystems(storage, mountOnly=flags.flags.dirInstall, callbacks=callbacks_reg)
  File "/usr/lib64/python2.7/threading.py", line 766, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/usr/lib64/python2.7/site-packages/pyanaconda/threads.py", line 238, in run
    threading.Thread.run(self, *args, **kwargs)
IOException: Partition(s) 2 on /dev/sda have been written, but we have been unable to inform the kernel of the change, probably because it/they are in use.  As a result, the old partition(s) will remain in use.  You should reboot now before making further changes.

Additional info:
cmdline:        /usr/bin/python2  /sbin/anaconda --liveinst --method=livecd:///dev/mapper/live-base
cmdline_file:   BOOT_IMAGE=vmlinuz0 initrd=initrd0.img root=live:CDLABEL=Fedora-Live-MATE-x86_64-22-20150 rootfstype=auto ro rd.live.image quiet  rhgb rd.luks=0 rd.md=0 rd.dm=0 
executable:     /sbin/anaconda
hashmarkername: anaconda
kernel:         4.0.0-0.rc1.git0.1.fc22.x86_64
other involved packages: pyparted-3.10.3-1.fc22.x86_64, python-libs-2.7.9-5.fc22.x86_64, python-blivet-1.0.3-1.fc22.noarch
product:        Fedora"
release:        Fedora release 22 (Twenty Two)
type:           anaconda
version:        Fedora