Initially proposed as [1], but then changed to comment fix only.  VMDK
can have internal version set to 2 when there are few features added
which do not affect us.  Thanks to Jan's commit a1ee8e18 this can be
easily fixed by adding it to list of supported versions.

[1] http://www.redhat.com/archives/libvir-list/2013-June/msg00419.html

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=836676