Description of problem:
I use pyanaconda.storage module outside Anaconda installer. I have an encrypted partition, mounted somewhere.

storage.devicetree.populate() fails with traceback:

  File "anaconda_init.py", line 25, in <module>
    storage.devicetree.populate()
  File "/usr/lib64/python2.7/site-packages/pyanaconda/storage/devicetree.py", line 1856, in populate
    self._populate()
  File "/usr/lib64/python2.7/site-packages/pyanaconda/storage/devicetree.py", line 1970, in _populate
    self.addUdevDevice(dev)
  File "/usr/lib64/python2.7/site-packages/pyanaconda/storage/devicetree.py", line 1086, in addUdevDevice
    self.handleUdevDeviceFormat(info, device)
  File "/usr/lib64/python2.7/site-packages/pyanaconda/storage/devicetree.py", line 1667, in handleUdevDeviceFormat
    self.handleUdevLUKSFormat(info, device)
  File "/usr/lib64/python2.7/site-packages/pyanaconda/storage/devicetree.py", line 1164, in handleUdevLUKSFormat
    self.__passphrases)
  File "/usr/lib64/python2.7/site-packages/pyanaconda/storage/devicetree.py", line 78, in getLUKSPassphrase
    raise RuntimeError("device is already mapped")

Version-Release number of selected component (if applicable):
anaconda-18.6.5-1.fc18.x86_64

How reproducible:
always

Steps to Reproduce:
1. cryptsetup luksOpen /dev/sda1 myLuks
2. try to populate storage.devicetree
  
Anaconda probably expects that it's running on 'unconfigured' system, where nobody opened LUKS device. If I 'luksClose /dev/mapper/myLuks', it starts working.

If Anaconda is to be used as storage library, this must be fixed.