"No such file or directory: '/var/lib/virt-who/key'" エラーが理由で virt-who サービスの開始に失敗する

Issue

• virt-who サービスの起動に失敗し、ログに以下のエラーメッセージが表示されます。

[root@example]# systemctl status virt-who
● virt-who.service - Daemon for reporting virtual guest IDs to subscription-manager
   Loaded: loaded (/usr/lib/systemd/system/virt-who.service; enabled; vendor preset: disabled)
   Active: failed (Result: exit-code) since Thu 2017-01-26 22:19:48 UTC; 2s ago
  Process: 121144 ExecStart=/usr/bin/virt-who (code=exited, status=1/FAILURE)
 Main PID: 121144 (code=exited, status=1/FAILURE)
   Status: "virt-who can't be started: [Errno 2] No such file or directory: '/var/lib/virt-who/key'"

Jan 26 22:19:47 example.com /usr/bin/virt-who[121144]: [ERROR] @main.py:127 - [Errno 2] No such file or direc...key'