Description of problem:
dnf needs pyliblzma in order to decompress xz repodata, but dnf doesn't Require pyliblzma.

Version-Release number of selected component (if applicable):
dnf-0.5.4-1.fc21.noarch

Steps to Reproduce:
1. dnf remove pyliblzma
2. dnf grouplist

Actual results:
Error: No group data available for configured repositories.

Expected results:
(groups listed)

Additional info:
Took me a while to figure out that the error message actually means that dnf silently failed to decompress the comps.xml.xz and therefore it sees no groups.