Failed at stage "init" beccause it could not parse "ip addr show"

Environment: Virtuozzo
Cloud provider: Strato AG Germany

Cloud-init was manually installed after first boot to simplify server setup.

Minimal cloud-init configuration which leads to failure:

  #cloud-config
  cloud_init_modules:
    - users-groups

  users:
    - name: username

Output of "ip addr show":

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: venet0: <BROADCAST,POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default
    link/void
    inet 127.0.0.1/32 scope host venet0
       valid_lft forever preferred_lft forever
    inet 85.214.226.67/32 brd 85.214.226.67 scope global venet0:0
       valid_lft forever preferred_lft forever
    inet6 2a01:238:427f:2300:c8a3:3e40:399f:3ddd/128 scope global
       valid_lft forever preferred_lft forever
    inet6 ::2/128 scope global
       valid_lft forever preferred_lft forever

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: cloud-init 18.4-0ubuntu1~18.04.1
Uname: Linux 4.15.0 x86_64
ApportVersion: 2.20.9-0ubuntu7.5
Architecture: amd64
CloudName: Other
Date: Sat Feb 16 02:34:53 2019
PackageArchitecture: all
SourcePackage: cloud-init
UpgradeStatus: No upgrade log present (probably fresh install)
logs.tgz: Error: [Errno 2] No such file or directory: '/tmp/cloud-init-logs.tgz'
modified.conffile..etc.cloud.cloud.cfg: [deleted]
modified.conffile..etc.cloud.cloud.cfg.d.05_logging.cfg: [deleted]
modified.conffile..etc.cloud.cloud.cfg.d.README: [deleted]
user_data.txt: Error: [Errno 2] No such file or directory: '/var/lib/cloud/instance/user-data.txt'