Description of problem:
Sometime in the last days, a change has been made to the installer such that already existing LVM volumes are not shown when custom partitioning is chosen.
Of course, this means that the installation has to be aborted at that point.

Version-Release number of selected component (if applicable):
anaconda-21.29-1.fc21

How reproducible:
Always.

Steps to Reproduce:
1. Boot system from boot.iso image.
2. Choose custom partitioning.

Actual results:
An existing volume group and its associated volumes are not shown in the disk partioning spoke whereas an existing ext4 boot partition is.

Expected results:
Show existing LVM disk layout and allow the user to assign appropriate mount points to the different volumes.

Additional info:
This used to work until for anaconda versions earlier than anaconda-21.29-1.