You'll need to make sure the kvm group has a gid > 1000.

E.g. edit /etc/group and change the kvm line from say 106 to 10666, then

# apt-get install --reinstall eudev

fails with:
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The group `kvm' already exists and is not a system group. Exiting.
dpkg: error processing package eudev (--configure):
installed eudev package post-installation script subprocess returned error exit status 1
Processing triggers for man-db (2.8.5-2) ...
Errors were encountered while processing:
eudev
E: Sub-process /usr/bin/dpkg returned an error code (1)
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